Tag: ReefKeeping

I’ve been doing water changes on my freshwater tanks for over 25 years, and for most of that time I’ve been routing that water straight to my garden instead of down the drain. As long as your tank is freshwater and hasn’t been medicated, that nutrient-rich water is liquid gold for plants — I’ve seen the difference firsthand. Here’s everything you need to know about using aquarium water on your plants and why it works so well.

Why It Works

Before we can see how fish tank water can be used to feed terrestrial plants, we need to understand what makes this water special. Like anything in the aquarium hobby, it all ties back to the nitrogen cycle.

I’ve always thought of my water change water as free fertilizer. Instead of dumping it, I walk it straight to my garden beds — my freshwater community tanks produce some of the richest free plant food you can find.

When you cycled your tank, you needed to introduce a source of ammonia into your aquarium. This could have been done organically or chemically. After a while, beneficial bacteria started to reproduce and process the ammonia into other compounds, like nitrite and nitrate. Once enough bacteria had populated the aquarium, ammonia and nitrite could be maintained at 0 ppm while nitrate was controlled through water changes.

Just because ammonia and nitrite aren’t readable in your current tank through test kits doesn’t mean that they’re not present though. In fact, fish are constantly creating ammonia through respiration and waste. Most test kits don’t read to this precision.

Plants and Nutrients

If you have a freshwater aquarium, you may have been recommended to add live plants to help cycle the aquarium and to keep an overall healthy system. There is a good reason for this! As we’ll see, aquatic plants are very similar to terrestrial plants in how they rely on nutrients; aquarium plants get most of their nutrients through the water column, though sometimes through the substrate, and most terrestrial plants rely on the soil to receive nutrients.

Plants can absorb all of these nitrogen compounds: ammonium, ammonia, nitrite, and nitrate. Most species uptake nitrate the most, but live plants can help maintain the other levels. This is why adding live plants to an aquarium can decrease the toxicity of the water and maintain levels in the future.

It’s important to note that freshwater aquariums also contain other important compounds, like magnesium and phosphate, that aren’t regularly tested for. Just because hobbyists don’t monitor these parameters doesn’t mean they’re not present in the aquarium. As we’ll see, they’re some of the most important compounds for growing terrestrial plants!

How can our fish tanks help our indoor plants and possibly even help grow the food that we eat?

Plant Fertilizer

The next time you go into an outdoor store or gardening center, take a look at the available fertilizers. You may see a variety of powder and liquid options, each of which will provide a percent breakdown of the nutrients offered.

You will likely see a ratio of three values on the front, which read N-P-K¹, or nitrogen-phosphorus-potassium. These are some of the most important nutrients for plant growth, and the ratio needed will depend on the species of plant being grown.

While you likely won’t get this precise ratio with fish tank water, nitrogen, phosphorus, and potassium are present in your aquarium. While nitrogen is predictable, phosphorus, potassium, and micronutrient levels will vary as they are influenced by tap water, food ingredients, and other inputs.

Now that we know how aquarium water acts as a fertilizer, how can we use what we have?

Watering and Water Changes

The best way to use your aquarium water as a plant fertilizer is by not wasting what you already have! More than likely, you perform water changes on your aquarium anywhere from once a week to several times a month. Chances are that you’ve been throwing that old water down the drain.

Before you get rid of that water, get a watering can! Use an aquarium siphon or cup to remove the water from the tank and into your container. As long as there isn’t a ton of fish waste or other organic debris, this water can be directly used to water plants. It really is as easy as that!

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The Python is a mainstay in the fish hobby. Easily clean your aquarium by connecting this to your sink!

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If you’re siphoning your substrate during your water change, then you may want to take some time to let that gunk settle at the bottom of your container. While it is unlikely to hurt your plants, fish waste left sitting on top of the soil can attract other garden pests and lead to a nasty smell.

But wait! Don’t throw that fish poop out either. In fact, this organic matter can be directly added to a compost pile along with any excess water.

Storing Water

Unless you have a ton of plants, you’ll probably end up with leftover water from your fish tank. This water can be discarded as usual, or you may consider setting up a reserve for later use.

This reserve is like setting up another fish tank but in a closed tub or bucket. Here is one way of setting up an aquarium water reserve:

Use a bucket, tub, or other large container. This container should not let light in as this will facilitate algae growth that will end up stealing nutrients. In the worst-case scenario, this nutrient-packed algae can be used for composting!

This container should also be closed so that no contaminants, like aerosols, insects, or a thirsty pet, can make their way in. If you use a trash cute, the Brute brand is a great mainstay in the hobby. Make sure it is labeled as food grade.

Use filter media. Contrary to popular belief, beneficial bacteria do not live in the water column. Instead, they live on the surfaces in our fish tanks, mainly in porous filter media. While new amounts of ammonia or nitrite are unlikely to enter your container, beneficial bacteria will continue to make your used fish tank water a healthy environment. You can also squeeze out your sponges during water changes to release some of the bacteria and the nutrients.

Install a pump. Even though this water will be processed by beneficial bacteria, stagnant water will still invite unhealthy microbes. Stagnant water will likely grow algae and other slime while also depleting the water of oxygen. This could create anaerobic conditions, which would not be healthy for ornamental plants.

Check your water regularly. Fish tank water won’t store indefinitely, and we don’t recommend hanging onto it for more than a week, especially if there is sediment or other organics present. If you notice a funky smell or any other signs of contamination, dispose of the water.

Indoor Plants In Your Aquarium

Aquarium water can be used to water plants with a watering can, but it can also be used straight from the source. Many hobbyists have begun growing indoor plants, and even some fruits and vegetables, straight out of their aquariums. This removes the need to store water and gives plants direct access to some of the best plant fertilizers available. In return, the plant helps remove excess nutrients from the water column.

In order to grow terrestrial plants out of your aquarium, you will need an additional grow light. Also, some plants cannot have constantly submerged roots, so some special selection is needed.

Considerations When Using Aquarium Water For Plants

Aquariums make some of the best plant fertilizers available, but you might have a few questions about keeping healthy fish and healthy plants.

Should you add more nutrients directly into your aquarium?

It would make sense that adding more nitrogen compounds and other nutrients to your aquarium would make your fertilizer even better, but aquariums have a delicate balance of parameters. Too much ammonia or nitrite can lead to poisoning your fish; even high levels of nitrates can eventually impact your aquarium.

However, many hobbyists add nitrogen additives to their aquariums to help their aquatic plants grow. In moderation, this is a great way to facilitate growth and even get more desirable colors out of your live plants. In terms of dosing other macro and micronutrients, like magnesium and phosphate, it’s generally not necessary unless you are certain your aquarium is lacking in them.

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Being able to water plants with fish tank water is an added benefit of your aquarium, not its main purpose (though we’ll discuss more in the aquaponics section later).

Should you be worried about aquarium chemicals?

Yes, there are some potential hazards associated with using fish tank water that has been treated with chemical products. This is especially a concern if using the water on edible plants.

Most hobbyists dose their fish tanks with at least one chemical. Most often, this is a dechlorinator that removes chlorine and chloramine to make water safe for fish, but can also include medications. However, most of these chemicals are not food-grade and cannot be ingested safely for certain. Some fish keepers use alternatives, like ascorbic acid, as a dechlorinator, but this takes some special measuring.

One product you might not consider a threat to plants is aquarium salt. Most plants cannot physiologically process salt and may start to die as a result. You should never use saltwater for a garden if you keep a marine tank.

⚠️ From my experience: The two setups I always warn people about are saltwater/reef tanks and African cichlid tanks. Reef tanks have obvious salt issues, but cichlid tanks also tend to run high pH and sometimes have added salt — both can damage or kill garden plants. Stick with a standard freshwater community tank and you’ll be fine.

If the tank has been medicated in the past or is currently being medicated, you should also not use the water on your garden.

In general, you should avoid using chemically treated fish tank water on plants you intend to eat.

Does pH matter?

So far, we have not discussed pH. Freshwater aquariums typically have a neutral pH of around 7.0, but some blackwater or cichlid tanks might have well above or below that. Most plants thrive in the neutral zone, though some species prefer acidic or basic conditions respectively.

Another important parameter to consider is alkalinity, or the ability of water to buffer changes in pH. This parameter is rarely discussed in freshwater aquariums, with general hardness being a bigger concern. However, a high alkalinity can also impede plant growth and start to affect the effectiveness of pesticides and other enhancers.

Aquaponics

If you’re serious about using your fish tank’s water to facilitate your plant growth, you might be interested in the greater field of aquaponics.

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This takes growing plants with fish tank water to a whole other level. Simply put, aquaponics is sustainable farming using a closed-loop system that is dependent on the nitrogen cycle: fish create waste and the plants uptake the nutrients. Plants are grown directly in the water for easy nutrient uptake without the need for soil.

Some plants that can be grown in these systems include lettuce, tomatoes, peppers, and herbs.

Conclusion

If you love aquariums and gardening, then there are many reasons to start using your tank water to feed your plants! Aquarium water is packed with important nutrients, like nitrate, that can fertilize your plants as needed. Avoid using water that has been chemically treated on edible plants, but save your water change leftovers for later use.

🌿 Want to learn more? This article is part of our complete Planted Tank & Aquascaping Guide — your ultimate resource for aquarium plants, aquascaping styles, substrates, and more.

Is your fish tank filter not working?

Aquarium filters are essential in this hobby, so when they stop working, you can expect some problems! But what should you do if your filter malfunctions? Well, don’t rush off to buy a new one too soon because there’s a good chance you can fix it yourself!

In this guide, I’m going to help you get your aquarium filter up and running again. We’ll start off with some pretty obvious stuff and progress to more technical issues, so read through until the end and you should have the solution you need.

Troubleshooting – First Steps and Clues

Are you sure it’s not working?

This may seem like a silly question, but some filters are almost completely silent so you really need to look or feel to know if they’re running. Look for water flow near the filter’s outflow to know if water is moving through the pump.

If you’re sure your filter is not running, it’s time to figure out why.

When did it stop working?

Doing a little detective work can help you figure out some potential causes of your fish tank filter not working.

Let’s take a look at a few scenarios:

• After a power outage: Some filters need to be primed each time you start them. So, if your power went out, you might be able to re-prime your filter and get it up and running again.
• After a power surge: Lightning strikes, tree falls, and power outages can all cause surges that could damage electrical equipment¹.
• Gradual loss of performance: If your filter has been weak or noisy for some time, it could be a sign of a clogged impeller or filter media. These problems tend to build up over time.

Fish Tank Filter Not Working – 5 Possible Causes

Finding the problem with your aquarium filtration system is much easier when you know where to look. Continue reading to discover five possible causes and what you can do to solve them.

1. Power Problems

Aquarium filters need electricity to run, so that’s the first place to look when your fish tank filter stops working. Before we go any further, I just want to remind you of something obvious: ELECTRICITY IS DANGEROUS. Please leave electrical work to trained professionals.

With that out of the way, let’s look at some safe tests that you can do.

• Check the power source

If your filter isn’t running at all, don’t be too quick to assume that the filter is the problem! The issue could also lie with your power supply, power strip, or any of the connections between your electrical panel and the filter itself.

Start by making sure the filter is plugged in at a power outlet. Some outlets have a dedicated on/off switch, so make sure that’s in the ‘on’ position.

If it’s definitely plugged in but still not running, your next step is to test the outlet. You can do this by unplugging the filter and plugging in a different electrical appliance like a lamp. If that doesn’t work either, your filter is probably not the problem.

• Check your power strip

Sometimes there’s nothing wrong with the power source or the filter. Your powerstrip might be faulty or need to be reset. Some power strips include a reset button that will need to be pressed after a power surge or overload.

• Inspect the cable

Electrical cables are pretty prone to damage, so it’s a good idea to visually inspect them for signs of wear or breaks. If you’re handy, you may be able to repair a worn cable yourself, but I recommend getting help from a pro if you’re not sure.

• Are you using a timer?

It’s best to set your aquarium lights on a timer to keep a regular day/night schedule. However, your fish tank filter should be set to run constantly.

It’s annoyingly easy to get your plugs mixed up during the aquarium cleaning process, and sometimes the solution is as simple as switching plugs! If this happens to you, consider putting a zip tie or some colored tape on your filter cable to help you identify it easily.

2. Clogged Filter

Your filter is designed to collect debris from the water, but sometimes, these waste particles build up to such an extent that they create blockages that prevent your filter from working properly.

• Rinse regularly

Many fish tank filters use a synthetic sponge material as a filtration media. These sponges do not need to be replaced until they begin to fall apart, although they do require regular maintenance to avoid blockages.

The dirt that collects in your aquarium filter media will reduce water flow and mechanical filtration, but you can avoid this by simply rinsing the sponge outside of your aquarium in some tank water. Avoid using chemicals or hot water when cleaning your sponge media as this can kill the good bacteria that are essential for proper filtration.

Check out my detailed guide to the aquarium cycle to learn more about beneficial bacteria and the nitrogen cycle.

• When to replace

Some filters are designed to use cartridges that must be replaced regularly. This type of media should be replaced at the intervals recommended by the manufacturer to avoid a reduced water flow rate. Filter floss is another filter media that clogs easily and will need to be replaced regularly.

3. Air Locks

Sometimes, air gets into the filter and causes an air lock which reduces your flow rate or even prevents your filter from moving water. This often happens when the filter intake is not positioned below the water’s surface, although it also occurs if you run an airstone near the intake. You may need to prime your filter to get it restarted, although the procedure will differ depending on the type of filter you have.

• Hang on back filters

Many hang-on-back (HOB) filters need to be primed before they can operate or they may be very noisy and fail to operate correctly. However, some models have self-priming technology.

To prime a HOB, simply fill the impeller chamber with water from the aquarium until it begins to flow through the outflow and back into the tank. Then, you can adjust the flow rate to suit your needs.

• Canister filters

Many canister filters have self-priming technology, but some must be manually primed using the built-in pump. You may also need to rock your canister filter back and forth or side to side to dislodge any air trapped in the impeller housing. These filters should be placed below your aquarium for best results.

4. Disrupted Water Flow

Each aquarium filter type works differently, but they are all designed to suck water from the aquarium and pass it through some sort of filter media. The obvious exceptions are sponge or under gravel filters that work with an air pump.

Your filtration system will not work properly if water can’t flow through the media as it should, so it’s important to inspect your filter and ensure that everything is clean and put together properly.

• Water intake obstructions

The water intake is a common source of problems since this is the first place where blockages can occur. Inspect the intake grid or tubes for obstructions like plant leaves or hiding snails.

Sometimes, the intake tube of your filter may become dislodged, which disrupts the flow of water through the system. Make sure this component is seated properly as it can make a huge difference.

• Flow valves and flow rate adjustment

Many modern aquarium filters come with an adjustable flow rate, so this is a good place to start if your filter just seems a little weak. Check out your user manual or look for a dial or lever to increase the flow rate.

Canister filters have valves on both the intake and output valves. Water will not be able to flow through the canister if either of these valves are shut, so make sure the tabs of each valve are in the open position, or at least open enough for water to pass through.

• Water level in the tank

Over time, water will evaporate from your aquarium, leading to a slow decrease in water level. If the level gets below your filter’s intake, the unit will begin to suck air, and it may overheat or malfunction. Keep your aquarium full with regular top-ups and water changes.

5. Filter Motor Problems

• Clogged impeller

Internal power filters, canister filters, and hang-on-back filters all have a part known as an impeller, and this is a very common cause of filter issues.

The filter impeller is the part of the pump that spins, creating a water current that sucks water through the filtration media and back into the tank. Sometimes, this crucial part becomes dislodged from its correct position or it may get clogged with gravel or wrapped up in fibers or hairs that prevent it from spinning.

• Impeller maintenance

You can usually access the impeller pretty easily without any special tools, but make sure the filter is unplugged before opening it up. Gently remove the impeller with your fingers or a pair of tweezers and clean it off, paying attention to the blades and the steel impeller shaft. You should also look for obstructions in the impeller housing and clean it out if necessary.

• Impeller replacement

You can often get your aquarium filter back up and running by simply cleaning out the impeller and housing, but eventually, you might need to replace some parts. Impellers don’t last forever, so order a replacement when yours becomes grooved, worn, or broken.

What To Do If You Can’t Fix It – 5 Helpful Tips

You’re going to need to take action if you’ve tried all the options listed above and you still can’t get your filter to run. Here’s what you should do:

• Aerate your aquarium water

Your aquarium is not going to crash instantly without a filter, although the situation can become more serious after a few hours.

In the meantime, use an air pump and air stone to oxygenate your aquarium water. This will help your fish breathe and supply dissolved oxygen to the beneficial bacteria that live within your substrate and on surfaces within the tank.

• Run a spare filter

I recommend keeping a cheap spare filter for this kind of situation, but it’s very important to use it correctly here. If you’ve got an idea of how aquarium cycling and the nitrogen cycle work, you’ll know that special bacteria live in the media in your filter and that it can take several weeks to build up a decent colony.

Put the media from your faulty filter into your spare until you can get a new filter or fit replacement parts. You may have to trim the old sponge down to size, but that shouldn’t be a problem. Bio balls and other media types can also be transferred to your spare filter if the design allows custom media.

• Buying replacement parts

You can usually buy replacement parts if you have a decent brand-name fish tank filter, although it may make more sense to buy a new filter in some cases. You can ask your local fish store to order replacement parts or simply purchase them online.

• What if you don’t have a spare filter?

It is possible to care for the beneficial bacteria in your old filter media, although it can get a little messy if the old media hasn’t been rinsed in a while. Gently remove the media and place it in the tank near an air stone to encourage some water movement through the media and keep the good bacteria oxygenated until you can get a new filter up and running.

Note that if you purchase the same filter to replace your broken one, you can swap the filter media into the new filter. This will help prevent losses in the bacteria colony as the colony will still function in the new filter.

• Running a second filter

Did you know that you can run two or even three filters in the same aquarium? Most aquarists will run a single powerful filter, although two smaller fish tank filters can provide adequate filtration while giving you that extra insurance in case one fails.

Understocking your tank and growing live plants are great ways to slow the build-up of nitrate levels in the long run, but you can also reduce your filtration needs by feeding your fish correctly. Uneaten food is a major cause of poor water quality.

Final Thoughts

Providing proper filtration is essential for maintaining a beautiful aquarium and healthy fish, so it can be pretty stressful when your equipment malfunctions. I hope the advice in this guide helps you fix your filter problems without ordering a replacement, but please keep safety in mind when inspecting electrical equipment.

🔧 Want to learn more? This article is part of our complete Aquarium Equipment & Gear Guide — your ultimate resource for filters, heaters, lights, pumps, tanks, and more.

I’ve been feeding vegetables to my fish for years — Nori sheets for saltwater tanks, and cucumbers and romaine lettuce for freshwater setups. It’s one of the most underrated things you can do for herbivorous and omnivorous fish, and once they find it, they go for it every time. One critical step most people skip: blanching. Leave it out and you risk fouling your water with pesticide residue and disintegrating plant matter. This guide covers what actually works, what doesn’t, and how to prepare it correctly.

Vegetables For Fish – Which Are The Best Ones?

The best vegetable to feed fish (video from our official YouTube Video) is one that will withstand being submerged, at least for an hour or two. This vegetable should not start to disintegrate once a hungry fish starts to get to it. Luckily, a variety of vegetable options can be blanched and eaten by fish.

A good list of rotating veggies might look like:

• Broccoli
• Cucumber
• Zucchini
• Yellow squash
• Spinach
• Romaine lettuce
• Carrot
• Peas
• Nori (great for saltwater fish)

Not all fish will like all vegetables, so it might take some time to figure out which ones to include in your feeding rotation. Most hobbyists like to weigh small pieces down with a rubber band around a rock or a suction clip that attaches to the side of the glass.

🏆 My personal picks: For freshwater tanks, cucumbers are my go-to — fish love them, they hold up well submerged, and they’re easy to prep. For saltwater, Nori (dried seaweed sheets) is the clear winner — tangs and rabbitfish will go absolutely crazy for it on a clip. I’ve also had great results with romaine lettuce in freshwater setups.

Does Your Aquatic Pal Need Them?

Before we even start to discuss how to prepare fresh vegetables for your fish, you need to know if these foods would be similar to something that they would naturally come across in the wild. A carnivorous fish will probably not eat a cucumber, no matter how appealing it might look!

Most likely, you won’t be able to tell whether a fish is a carnivore, herbivore, or omnivore just by looking at it. There might be some signs, like sharp teeth or a sucker mouth, but even then, you can’t be fully sure. The best way to find out the natural diet of your fish species is by doing research about their natural habitat and hearing experiences from other hobbyists or your local aquarium store.

Once you’ve established the natural diet of your fish, you can begin catering to it. If it turns out that you have a herbivore fish, then you might start to supplement blanched vegetables into their diet.

Benefits of Veggies

There are many benefits to giving vegetables to fish. The main benefit is keeping fish healthy by supplementing vitamins and minerals that aren’t supplied through typical fish food¹.

The other main benefit is enrichment. By now, you’ve probably noticed that your fish waits to be fed at the top of the aquarium anytime you walk by. Feeding time is what they look forward to! Adding veggies is a great way to make feeding time even more exciting and unpredictable while also adding variety and balance to your fish’s diet.

What Are Blanched Vegetables?

Simply put, blanching means submerging vegetables or fruits into boiling water for a short period, quickly removing them, and then placing them into a bowl of water with ice. This process only takes a couple of minutes but helps preserve the quality of the vegetable or fruit.

There are a few ways blanching achieves preservation. First, it inactivates enzymes that would otherwise begin to affect color, taste, and nutritional value over time. Similarly, blanching affects bacteria which would also cause the product to degrade faster.

Blanching is especially recommended when using vegetables as fish food due to insecticides and other residues. Unfortunately, many unknowns are used to treat food for consumption, so boiling them first reduces the chances of those chemicals entering the aquarium.

⚠️ The biggest mistake I see: People skip blanching entirely. Raw, unblanched vegetables can foul your water fast as they break down, and you’re putting pesticide residue directly into your tank. Blanching takes about two minutes and makes a real difference — don’t skip it.

All in all, blanching fresh fruits and vegetables helps preserve them for longer and allows for easy freezing and storage. In the aquarium setting, most hobbyists only offer vegetables as fruits can be messy.

Can You Serve Them Raw?

Yes! Tropical fish can be fed raw vegetables. Blanching is recommended for hobbyists who want to keep vegetables on hand for future use. There are a couple of things that need to be considered, though.

As mentioned before, veggies are often treated with chemicals and other preservatives. These should be thoroughly washed off before being added to the tank. It is also likely that these pieces of raw vegetables will end up floating on the surface of the water, so it might take some extra effort to weigh them down.

How To Blanch Them

Almost any vegetable can be blanched, but not every blanched vegetable is good for the aquarium. Instead, certain hard vegetables, like broccoli, cucumber, zucchini, and peas, are some of the favorite feeding options for herbivores. This is because other vegetable matter can easily break down and start to affect water quality.

Vegetables with strong aromas, like brussels sprouts and onions, should be avoided as they can start to affect water conditions as well.

Buying Them

This might seem obvious, but you need to purchase your vegetables at the grocery store. Your local fish store will not have fresh vegetables! Now the question comes down to picking the right veggies for your fish.

Should you buy organic?

You definitely want to pick the best vegetables possible to feed your fish, and you should be mindful of what you’re putting in the aquarium. However, there is likely little difference between buying organic and using regular produce. The blanching process should hopefully remove any chemicals or additives in either option.

If you want to feed raw cucumber or another vegetable fresh from the rack, then it may be the better choice to buy organic.

Preparation

Depending on what type of vegetables you get for your fish, you might need to do some prep work. Think about how much food you want to give to your fish, for how long, and if you could use the leftovers for your own consumption!

Some vegetables, like zucchini, cucumber, and broccoli, will need to be cut up into manageable pieces. The goal should be to slice to expose as much of the soft, inside flesh as possible as fish will likely eat these sections first. For something like zucchini, slice each piece to be about 0.5 inches. Most other vegetables, like spinach and lettuce, can be split apart and fed more easily.

Now, you will want to consider how long you want to serve your fish this food. Fish eat as much as is available, so it’s not recommended to give it all at once. But you don’t want to be feeding the same thing for a month either! Prepare enough food for several feedings. Save some for blanching and save some for the dinner table.

Blanching Steps

Now it’s finally time to blanch the veggies. This process is straightforward and easy and almost impossible to mess up.

1. Bring a pot of water to a rolling boil. The boiling water will activate those processes we talked about earlier!
2. Fill a separate bowl with water and ice.
3. Add the sliced vegetables to the boiling water.
4. Allow them to boil for 1-3 minutes depending on the size of the slices.
5. Remove the vegetables when they’re crispy. A crunchy vegetable needs more time and a mushy vegetable has gone too long.
6. Add the veggies to the ice bath. Let them sit in the cold water for a minute or two.
7. If you’re planning on freezing the vegetables, then wait until they’re completely cooled and dried. Then, store them in a plastic bag in the freezer.

Feeding Your Fish

When you’re ready to feed your fish, make sure to fully thaw the frozen vegetable matter. You may need to weigh it down with a rock or clip so that it doesn’t float.

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Allow your fish to eat. It might take some time for them to find and understand that the vegetable matter is food. Snails are also naturally slow!

After a couple of hours, remove what remains of the veggies. If your fish and snails liked what they were given, you might just find vegetable skin left over.

How Often To Feed Vegetables?

How often you feed your fish fresh or frozen vegetables will depend on how many fish are present and their feeding habits.

If you have a larger tank with lots of tropical fish, shrimp, and snails, then you will need more food to make sure that everyone is getting fed. Always make sure to keep an eye on uneaten food and remove any pieces that could potentially get stuck in the back of the tank.

In general, fresh and frozen vegetables can be given one to two times a week to create a well-balanced diet.

Alternatives

While most aquarium fish enjoy a veggie snack every now and then, some fish simply don’t like vegetables, even if they’re herbivores.

It makes sense why a carnivorous fish might not eat veggies, but why wouldn’t a herbivore?

It is possible that your fish was never introduced to any foods other than flake or pellet foods. They might not know how to eat veggies! In cases like this, you can continue to offer your fish fresh vegetables until they take a nibble, or you could settle with a high-quality algae wafer or pellet.

For saltwater fish, consider a product like Julian Sprung’s Sea-Veggies

Great For Algae Eaters

Sea Veggies Seaweed Green

Sea veggies is an amazing product for Tangs, Rabbitfish, and Marine Angelfish. Fish go crazy for it. Clean and easy to feed!

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FAQs

Conclusion

Most fish love a selection of fresh veggies in addition to their staple fish flakes or pellet, though some fish don’t! These vegetables can be served raw or blanched and frozen for later use. Some options include lettuce, peas, carrots, and broccoli, but an algae wafer will substitute for more picky fish.

Keep in mind that feeding fresh veggies can be messy and not all fish will enjoy the offer! Uneaten food should be removed if left untouched after a couple of hours.

🐟 Want to learn more? This article is part of our complete Aquarium Care Guide — your ultimate resource for water chemistry, maintenance, feeding, disease prevention, and everything you need for a healthy tank.

I’ve been keeping fish for over 25 years, and few things in this hobby beat the moment a tank design truly clicks. Aquascapes, cichlid rockscapes, and nano planted betta tanks have all inspired setups in my own fishroom over the years — and they still do. If you’re looking for your next build or just some inspiration for what’s possible, this is one of my favorite topics to cover. Here are 30+ fish tank ideas from across the hobby that I keep coming back to.

Nano Fish Tank Ideas

In the aquarium hobby, small aquariums are usually referred to as nano tanks. How small is small? Well, the definition varies, but you can call anything smaller than about 20 gallons a nano tank.

There are many different nano tank styles, ranging from species-only setups to thriving communities. Continue reading for some nano tank inspiration!

10-gallon Nano Betta Fish Tank Idea

Betta fish are one of the most popular nano fish in the hobby, but we see them in tiny bowls and other containers way too often. This beautiful 10-gallon nano betta fish tank deserves a round of applause¹!

The combination of live aquatic plants, driftwood, hardscape, and a little beach area gives this tank a feeling of balance and tranquility. I bet that’s one happy betta.

5-Gallon Betta Setup

You can also go a little smaller for a single betta, although you’ll still need a filtration system and a heater. Maintaining high water quality will also become more challenging, but regular water changes and cleaning will keep your fish happy and healthy.

At 5 gallons, this well-planned fish tank is about the smallest you should go for bettas or other live fish. However, you can make a nano tank look much roomier than it really is by decorating it carefully.

Notice how the dark substrate makes the plants stand out even more? Black sand or gravel can also make fish look brighter and it’s great for some shy fish species that prefer a dark habitat.

🏆 My Pick: If I had to recommend one starting point for beginners who want to build something beautiful without overwhelming themselves, it’s the natural planted betta tank. The footprint is small, the cost is manageable, and the results can look incredible. I’ve set up many of these over the years and they never get old — it’s the best entry point into seriously impressive aquarium design.

Community Aquarium

It is possible to keep multiple nano fish species together in a small tank, but you’ll need to step up to an aquarium in the 15 to 20-gallon range to house your fish safely.

This elegant tank is home to multiple fish species and some beautiful aquatic plants. Most fish that grow to about 2.5 inches or less can be kept in this tank size, although it’s important to research the minimum school size and parameters of each species.

Themed

There are some awesome aquarium decorations out there for setting up a themed fish tank. Check out these fun but contrasting examples from across the web!

Spongebob

Spongebob-themed aquarium decorations can turn a nano tank into a fun and exciting fish tank, especially for the kids. This themed aquarium looks just like a scene from the popular TV show, and those yellow fish fit right in!

Bamboo Forest

Looking for something a little more zen? Check out this peaceful betta tank, complete with its own bamboo forest. This fish tank theme is perfect for your work desk, especially if you have a stressful job.

Planted Aquariums

If you ask me, all freshwater aquariums should include some live plants! Live plants have many benefits for your fish, and they look great too! Let’s take a look at some amazing planted tank eye candy.

Submerged Bonsai

Plants dominate this incredible aquascape, although its creator has chosen to create a scene that looks more like a dry landscape than an underwater scene!

It would take many years to grow an actual bonsai that looks this good, but by cleverly planting a small plant like Anubias barteri var. nana on a great piece of driftwood, you can achieve much faster results.

The addition of carpet plants and that inviting clearing under the ‘tree’ make this peaceful scene really aesthetic. Can you picture a few shrimp or a betta hanging out under the shade of those branches?

Dutch Style

This amazing Dutch style planted fish tank ticks all the right boxes for aquarists who like a lot of color! This orderly aquascaping style requires dedication and a real eye for design, but the results are incredible.

⚠️ A Word of Caution: The biggest mistake I see people make when trying to recreate a tank they found online is skipping the research on plants and aquascape layout concepts. Aquascaping has its own language — rule of thirds, foreground/midground/background layers, plant selection based on light and CO2 requirements. If you dive in without understanding these principles first, you’ll spend a lot of money on plants that die and layouts that fall apart. Study the style you love before you buy anything.

The rimless tank and open-top design add another dimension of viewing pleasure to this tank. Sometimes, plants look the best when viewed from above!

Dutch-style planted tanks are all about the plants, but that doesn’t mean you can’t add some movement. The vertical bars on those angelfish really complement this tank!

Emersed Growth

There’s something special about a planted tank with emerging plants. This stunning aquarium is a true underwater paradise, complete with lush vegetation growing out of the water, just as it does in nature.

Many common aquarium plants, including Ludwigia and Rotala, can be grown emersed in a hoodless tank with suspended lighting.

Fish safety is an important consideration when planning an open-top fish tank. Fish are surprisingly good at jumping out of tanks, so it’s a good idea to cover the top with some kind of screen.

Paludariums

Giving your plants the freedom to grow up and out of the water creates a unique look, but you can go even further and create a truly amphibious tank. Paludariums, like this exquisite example, include an underwater section and a land section.

Depending on the size and design of your paludarium, you could house aquatic life like fish, shrimp like red cherry shrimp, or dwarf frogs in the water. The land section is great for frogs, and turtles that like to spend time in and out of the water.

The land section of your paludarium could take the form of an island that sticks out of the water in the center, or you could add a simple shelf, complete with some rocks, soil, and plants.

The Living Wall

A planted wall is another spectacular design, although this limits some of the animals you can keep. This example provides some swimming space for shrimp or nano fish, and plenty of planting space for those awesome tropical plants.

African Cichlids

African cichlid tanks are the ultimate choice for freshwater aquarists who want a large tank that bursts with color and movement. Although you can grow some plants in African cichlid tanks, these setups are usually all about the fish.

Rock Pile

Some fishkeepers house African cichlids in pretty open, bare-bottom fish tanks, but if you ask me, these fish look so much better with some dramatic rocky hardscape!

This tank creates wonderful cichlid habitats and makes a bold statement as a display tank. The white sand contrasts with the round rocks to make this simple but effective tank really pop.

Just make sure you secure round rocks properly if you set up a tank like this, they could easily injure your fish or crack your tank if they come tumbling down.

Rock Walls

When we talk about aquarium hardscape, most people think of arranging and stacking rocks or driftwood on the bottom of the fish tank. However, the back and side walls can be used to create an amazing effect.

You could simply use a life-like stick-on aquarium background, or go this route and create something with real texture!

Angelfish

Angelfish are stunning freshwater cichlids that come from South America. These distinctive fish have a very ‘tall’ body shape, so they need a tank with some real height.

These fish thrive in planted tanks and can be housed with many other peaceful community fish in a big enough aquarium – just avoid tiny tank mates that your angels might see as a tasty snack.

Altum Angel Aquarium

This gorgeous designer fish tank is home to a big group of Altum angelfish, a large species native to the Rio Negro and Orinoco rivers in South America. The dramatic driftwood contrasts against a backlit background to make an aquarium that no one is walking by without stopping to stare!

Aquascapes

Most aquascapes include live plants, but you can also create a stunning scene by arranging hardscape features like rocks and driftwood. Let’s take a look at some interesting aquascapes.

Forest Scapes

This inspiring aquascape looks just like a forest scene from the great outdoors, complete with mountains! This kind of project takes real dedication and a lot of experience, but the results are absolutely amazing.

Iwagumi

This iwagumi masterpiece by George Farmer highlights the simple beauty of this unique aquascape design. Each rock is carefully arranged in the frame to create a simplistic yet bold look, and the dense carpet of plants only adds to its appeal.

This type of fish tank looks best with a small group of schooling fish like neon tetras, which create the effect of a flock of birds flying over the aquascape.

The Nature Aquarium

This jaw-dropping tank is a prime example of a nature aquarium. The style was popularized by the legendary Takashi Amano, a pioneering aquascaper from Japan. The style aims to create a unique natural world, rather than recreating a scene directly from nature.

A variety of different plant types are used in this style, but hardscape features like rocks, roots, and driftwood are equally important in creating different zones and textures in the tank.

Glofish Tanks

Have you ever heard of Glofish? These neon-colored fish were originally genetically modified to identify toxins in water, but today they are very popular in the aquarium hobby for their vibrant colors.

Neon Glow

Glofish come in exotic colors like sunburst orange, electric green, and galactic purple, and they include popular species like corydoras catfish, tetras, danios, and rainbow sharks. These fish really stand out under blue LED lighting, and so do the special glofish gravels, aquarium decorations, and artificial plants.

Nano Glofish Setup

Glofish tanks are a perfect idea for the kid’s room or anyone who loves bright colors! This low-maintenance example shows off the amazing colors you can achieve with the right lighting and some cool glofish tetras.

Goldfish

The goldfish is another freshwater species that looks nothing like their wild ancestors. Hundreds of years of selective breeding have created the amazing variety of fancy goldfish breeds we know today.

Some people still think goldfish can live in little fish bowls, but these fish actually grow surprisingly large, so they need a fish tank of at least 30 gallons for long-term care.

Keeping goldfish is all about the fish. These adorable underwater pets have a long lifespan, and it’s really rewarding to watch them grow and thrive in a healthy fish tank.

The Minimalist

Many aquarists choose to keep their goldfish in open, minimalist tanks like this setup because they are easy to clean and place all the attention on the tank inhabitants. The addition of that long airstone adds another layer of interest to this fish tank while increasing oxygen levels in the water.

Eastern Elegance

This 60-gallon goldfish aquarium still has a low-maintenance design but includes a little more structure, including some great aquarium decorations that reflect the goldfish’s east Asian origins.

60 gallons is a great size for two or three fancy goldfish, and you could even consider some goldfish tank mates in a tank of this size.

Check out my guide to 11 goldfish tank mates for some great goldfish companions!

Nature Style Goldfish Aquarium

Unfortunately, goldfish love to snack on most plants, but that doesn’t mean you can’t create a natural home for your fishy friends. Some attractive river stones and soft artificial plants or tough live plants like Java fern and Anubias look great in a goldfish tank.

Big Tank Inspirations

Most of us can only dream of the kinds of tanks in this next section. Oh well, it doesn’t mean we can’t drool over them! Keep reading to learn about some amazing aquariums from across the world.

Outdoor Koi Pond with Glass Front

Don’t have space in your home for a big fish tank? These fish-lovers went ahead and designed a Koi tank/pond hybrid, which combines the best of both worlds!

Large koi are traditionally viewed from above, but this stylish setup allows you to enjoy your fish from every angle.

Kanye West’s Bathtub Aquarium

Stepping back inside, Kanye West’s super-stylish bath-tub tank is a great example of creative aquariums.

This tank helps you feel like you’re swimming in nature, every time you take a bath. The tank is filled with some awesome fancy goldfish.

The Mirage

Now, if money or space isn’t a problem, you might want to go with an aquarium like this beauty from the Mirage in Las Vegas. This mega 20,000-gallon fish tank is home to over 80 species of saltwater fish from tropical waters across the globe.

Atlantis The Palm

Some hotels go one step further, and let their guests view their amazing aquariums from within their suites! The Lost Chambers Aquarium in Atlantis Dubai allows viewers to enjoy sightings of over 60,000 ocean animals in the Ambassador Lagoon, all from their own suite!

Final Thoughts

So there you have it, 25 fantastic fish tank ideas that you can use to design your next aquarium. You could choose a nano-themed aquarium filled with cool decorations, an aesthetic nature aquascape full of aquatic life, or splash out on an impressive celebrity-style installation – the choice is yours!

Which of these 25 fish tank styles do you like the most? Share your view in the comments below!

🔧 Want to learn more? This article is part of our complete Aquarium Equipment & Gear Guide — your ultimate resource for filters, heaters, lights, pumps, tanks, and more.

Over the years, I’ve had countless customers reach out to me in a panic — fish dying, tank cloudy, water parameters all over the place. Most of the time, they’d skipped cycling or didn’t even know what it was. Fish-in cycling is the method you use when there’s no other choice and livestock is already in the tank. It’s not ideal, but it’s survivable if you know what you’re doing. Here’s exactly what I walk people through when they find themselves in this situation.

The Aquarium Cycle

The aquarium nitrogen cycle is a complicated process in which bacteria grow and populate an aquatic system to sustain life. Bacteria take toxic ammonia and nitrite levels and convert them into safer nitrates. Cycling an aquarium without fish can take up to 6 weeks, but is usually finished between 2 to 4.

The main reason why hobbyists wait to add fish until after the nitrogen cycle is because fish create a large amount of ammonia through waste and respiration. This becomes a problem as the population of bacteria in a new aquarium can’t keep up with the demand. As a result, ammonia levels spike, followed by nitrite levels, and eventually nitrates. This can lead to water parameters literally off the charts!

Even when an aquarium is freshly cycled, most hobbyists wait several weeks or months for the tank to reach stability, only adding a couple of fish here and there. This ensures that the bacteria populations grow alongside the increasing influx of ammonia.

Reasons Why It Isn’t the Best Practice

While fish-in cycling is generally looked down upon in the aquarium hobby, it can sometimes be an honest mistake. Unfortunately, many new hobbyists are eager to start their tanks and rely on only one source of information or don’t do any research at all!

If the only source of information is an employee at a local pet store, then the information might be incorrect or outdated. This is especially true if the employee works based on commission, where they are especially eager to sell the new hobbyists as much as they can, including a bag full of fish. Lack of research can also lead to impulsive buys and sudden fish deaths.

Are there any benefits to fish-in cycling?

No, there aren’t any benefits to fish-in cycling. An aquarium can only complete the nitrogen cycle with time and other methods won’t make a bacteria population grow any faster.

If you’ve already started fish-in cycling though, then you’ll want to be prepared for the next steps.

How To Successfully Pull Off Fish In Cycling (In 7 Steps)

Remember, it’s not recommended to do fish-in cycling for your aquarium, but it’s best to be prepared if you find yourself in this situation.

Here is how to handle an uncycled tank safely that already has fish in it!

1. Test Water Parameters

The most important aspect of any aquarium cycling is testing water parameters, even more so for fish-in cycling as fish can easily be affected by unsuitable conditions. In a fishless cycle, water parameters can largely be left uncontrolled, but fish need stability and nontoxic conditions.

While there are no acceptable ammonia and nitrite levels for fish, it’s best to keep both under 1.0 ppm to keep fish safe; this should be enough to keep the nitrogen cycle going while making more tolerable conditions for your fish.

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Along with ammonia and nitrite, nitrate levels should also be tested daily. Nitrate might take longer to appear in the aquarium as it’s one of the last compounds created by the nitrogen cycle. In general, nitrate levels can reach moderately high levels before they become toxic to fish, but a water change will be needed to reduce levels once past 20.0 to 40.0 ppm.

Another crucial water parameter to test is pH. Water’s pH can be difficult to control, and it’s usually best to leave it untouched. However, if your tank is experiencing daily swings of 0.5 to 1.0, then some moderation will be needed.

2. Water Changes

More than likely, you will need to do many water changes between the time of the first fish being added and several weeks after the cycle has officially finished. Water changes are the best way of having an immediate effect on water parameters, so long as the source water is reliable.

Depending on what your testing kit reads, you may need to do water changes once or twice a day until the parameters stabilize. How often a water change is needed will depend mostly on ammonia and nitrite levels, but nitrate can also become deadly at high levels and under extended exposure.

If you find your aquarium has nitrite or ammonia levels above 1.0 to 2.0 ppm, then a water change is needed. However, a large water change can also stress out fish and disrupt beneficial bacteria even more than they already are. Because of this, it’s recommended to do smaller, more consistent water changes.

In general, one or two 25% water changes throughout the day will help keep levels manageable, though this will be different with every fish tank. If ammonia, nitrite, or nitrate levels skyrocket, then it may be necessary to complete a near-100% water change.

Keep in mind that bacteria mostly colonize filter media and don’t live in the water column, so replacing the water is safe as long as the source water is safe.

3. Source Water

Understanding your source water is important for all stages of your fish tank’s life. Whether you decide to use tap water, distilled water, RO water, or RO/DI water, you should always know its baseline parameters.

Unfortunately, many tap water options contain ammonia as a byproduct of chloramine treatment. Products like Seachem Prime can help detoxify harmful compounds. Increasing or lowering pH may also be necessary depending on the origin of the tap water.

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4. Add Fish Slowly

The worst thing you can do for any new tank is add too many fish too quickly. Adding a lot of fish at once causes ammonia spikes due to the additional bioload and the bacteria’s inability to process increased amounts.

⚠️ The #1 Killer: In my experience helping customers through this, overstocking is the thing that turns a manageable fish-in cycle into a full wipeout. Too many fish means too much ammonia, and beneficial bacteria simply can’t multiply fast enough to keep up. If you’re stuck cycling with fish, fewer fish in the tank dramatically increases your chances of pulling it off. If that means temporarily rehoming some fish, it’s worth it — you can add them back once the cycle is established.

Adding a few hardy fish that can withstand less than ideal aquarium conditions is also a good way to give your tank a better chance of surviving its first few weeks. If able, add new fish the second day after the tank is set up. This will allow for some parameters, like water temperature, to stabilize. Even then, it is likely you will lose a few fish.

If you’ve already added all the fish you’re ever going to get into a brand new, day-one, uncycled tank, then you will want to test water parameters daily–if not several times a day–and follow the other protocols on this list.

5. Feeding

Another way to make the cycling process safer is by limiting feeding. During this time, fish will naturally be stressed and won’t need to eat as often as they usually do. Limiting the amount and frequency of feeding also has a few other benefits to keeping toxic levels down.

In any established tank, overfeeding can cause ammonia or nitrite to spike. This is because uneaten food breaks down like any other organic in the aquarium, causing it to contribute to ammonia, nitrite, and nitrate levels. This is also why leftover food should be removed from the tank within 5 minutes of being offered. To help prevent overfeeding and increasing waste load, only a flake or two should be offered at any given time.

Even though your fish might ask you for food, most aquarium species are hardy fish that can easily go several days without feeding. For an uncycled aquarium, it’s recommended to only feed one small portion every other day. This will also naturally decrease the amount of waste entering the system as less fish food is being processed.

6. Add Plants

Aquatic plants benefit any freshwater system, but they’re especially helpful when trying to keep toxic compounds out of an uncycled tank. The main reasons for having a planted tank include processing waste, increasing oxygen levels, and introducing pre-established beneficial bacteria colonies.

In order to grow, plants process nutrients from the water column and the substrate. These essential nutrients just so happen to be nitrate and some parts of ammonia and nitrite. Plants can be used to decrease the impact of ammonia buildup, though how much will depend on how many plants are added. There are also some plants that are more suited for nutrient reduction, such as Azolla, Hornwort, and Watersprite

A planted aquarium will also have more available oxygen than one without plants. In addition to nutrients, live plants also require carbon dioxide to complete photosynthesis. Oxygen is a byproduct of this process and is introduced into the water column. Additional oxygen is crucial for fish experiencing ammonia or nitrite poisoning as those compounds can start to burn the gills and affect breathing ability.

Lastly, adding plants will help transfer some beneficial bacteria from one cycled aquarium to an uncycled one via plants. Many bacteria will be lost in the transfer, but some should be able to be established in the new uncycled tank. This should help increase beneficial bacterial growth and population.

7. Add Beneficial Bacteria

Bottled beneficial bacteria is a relatively new product available at most local fish stores. Often, these products are advertised as being able to instantly cycle an aquarium, making conditions safe for the immediate addition of fish. While bottled bacteria should help introduce bacteria into the aquarium, it doesn’t guarantee that they’ll actually grow.

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The idea behind bottled beneficial bacteria is that you’re instantly introducing a colony of bacteria that can process fish waste and other contaminants¹. This doesn’t mean that you’re skipping the nitrogen cycle, but rather that you’re facilitating the bacterial growth necessary to complete it.

For some tanks, this works. But for others, it’s a false promise. While it won’t hurt your aquarium to dose beneficial bacteria during the cycling process, continue to follow the other recommendations on this list for extra security.

🏆 Mark’s Take: When customers call me in a panic about an uncycled tank, my three-part answer is always the same: dose a quality bottled bacteria product, stay on top of daily water changes to knock back ammonia, and reduce your fish load if you can. Those three things together give you the best shot at getting through this without losing fish. Don’t try to ride it out with just one of the three — you need all of them working together.

Other Tips And Tricks

The best way to safely make it through having fish in an uncycled tank is by monitoring it and making changes gradually. Remember that making big changes on top of already stressful conditions will only make things worse.

A few tips to getting through an uncycled fish tank emergency, on top of the other methods on this list, include: adding filter media from another cycled aquarium and asking your local fish if they’ll hold your fish for you.

As mentioned before, most of the bacteria that live in an aquarium grow within the filter cartridge and media. The easiest way to introduce, and sometimes even complete aquarium cycling, is by transplanting media from an already-established tank to the new one.

Some hobbyists also transfer ‘aquarium gunk’, which is the sludge-like organic matter often at the bottom of the tank or filter, which is teeming with biodiversity and bacteria. This transfer will effectively allow beneficial bacteria to continue processing the new tank just as it was in the previous one.

If everything on this list fails and your new fish are gasping for air, then it might not be too late to ask your local fish store or a fellow hobbyist for help. Many aquarium stores are willing to help out their patrons in regards to quarantining a few fish. They may provide a space for fish to stay while the aquarium cycling continues. If not, a fellow hobbyist may also have the means to make accommodations.

FAQS

Final Thoughts

It is never recommended to add fish to a completely new tank, but you might not have known or were given bad information. Luckily, there are a few ways to mitigate the harsh effects of ammonia, nitrite, and nitrate created by more fish waste and respiration. Some of these methods include water changes, limited feeding, and dosing bottled bacteria. If all else fails, you may ask your local fish store or a fellow hobbyist to hold your fish while the cycle continues.

KH comes up constantly in this hobby, and my approach to managing it has evolved quite a bit over 25 years of keeping both freshwater and reef tanks. In a reef setup, it’s about regular supplementation to keep levels stable — the coral depends on it. In freshwater, the smarter play is usually to stop trying to fight your source water and instead match your fish to what naturally comes out of the tap. That shift in thinking — from “how do I fix my water” to “what fish work best with my water” — makes the hobby a lot less stressful and a lot more successful.

What Is Aquarium KH?

Aquarium KH measures the concentrations of carbonates and bicarbonate ions dissolved in water. These concentrations vary depending on the geology of your area, so your tap water may have different levels to the next state or town.

You can measure and adjust your KH levels at home using products that are easily available at pet and local fish stores. A range of about 4-8 degrees or 70-140 parts per million is generally recommended for most freshwater aquariums, although different fish and plants have different water parameter needs¹.

Why Does It Matter?

Minerals are essential for fish health, but they also play a vital role in regulating your aquarium water chemistry. The minerals that determine your KH levels ‘absorb’ natural acids and prevent them from changing your water chemistry.

Author Note: You can think of KH as a sort of safety net for your aquarium. Without the buffering effect of KH, acids in the water can have immediate effects on your water chemistry, and that can be harmful to your fish.

So, the higher your KH, the more potential it has to neutralize or ‘buffer’ acids in the water before they can affect your pH.

What Is The Difference Between KH and GH?

GH (general hardness) is another important water chemistry parameter that is often confused with KH. While KH is a measure of carbonate and bicarbonate ions, GH describes the levels of magnesium ions and calcium ions dissolved in the water.

General water hardness does not have such a direct effect on pH levels, although hard water typically measures higher on the pH scale.

What is pH?

pH (short for ‘Potential of Hydrogen’) is a chemical measure of the acidity or basicity of a liquid. All liquids have a pH level, including your tank water.

The pH scale ranges from 0 to 14. Aquarium water between 0 and 6 on the pH scale is acidic, and from 8 to 14 is basic. Neutral water is right in the middle at 7 on the pH scale.

You can measure pH at home using an aquarium test kit, and it is possible to adjust your pH levels, although it’s better to aim for a stable pH than to chase a specific number on the scale.

Why Does pH matter?

Each fish and aquatic plant species has a preferred pH range, although many species are pretty adaptable as long you can maintain a stable pH.

Some aquarium fish do well in pH levels as low as 5 (discus) and as high as 8+ (African cichlids), but most freshwater fish prefer a stable pH level between roughly 6.5 and 8.

Maintaining a stable pH level can be difficult if your water has a low KH or buffering capacity, and rapid swings in pH can cause major stress on your fish.

What Affects pH Levels?

KH and pH are usually related in the aquarium, so if you have a low KH, you’re likely to have a low pH too. If you’d like to adjust your pH to keep specific fish species, you’re going to need to change your KH first.

pH levels tend to decrease over time, and the change can happen gradually or even suddenly in the case of a pH crash, but what causes these changes in water chemistry? Let’s take a look at four common causes of aquarium pH shifts.

Nitrates

You’re probably familiar with the aquarium nitrogen cycle, and how beneficial bacteria in your filter convert ammonia from fish waste into nitrite and nitrate. Well, nitrites and nitrates are acidic, which means they lower the pH of your water.

The best way to manage the nitrates in a fish tank is by performing regular water changes to remove them from the system, but you can also reduce the build-up by understocking your tank, growing live aquatic plants, and avoiding overfeeding.

Tannins

Have you ever added a piece of driftwood or some almond leaves to your tank, only to see the water stain yellow or brown?

Indian Almond Leaves

These leaves can be added to your aquarium to help promote a natural habitat for bettas, shrimp, and other soft-water loving fish. Betta breeders can use these leaves to help encourage breeding behavior.

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Tannins are acidic chemical compounds found in plants that can leach into the water, causing the ‘black water’ seen in many tropical freshwater environments. The effect is usually pretty weak, but tannins can reduce the pH in a freshwater aquarium, especially if you have low KH levels.

Carbon Dioxide

Carbon dioxide is acidic, which means it lowers the pH of aquarium water. Many aquarists use pressurized CO2 to increase plant growth, which is perfectly safe as long as the system runs on a timer to switch off at night when plants no longer photosynthesize. During the night, pH levels rise as the CO2 leaves the system.

Substrates and Rockwork

Crushed coral or dolomite substrates and limestone-based rock work like texas holey rock can increase the pH of acidic water.

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How To Test Carbonate Hardness

So now you know why KH is so important for maintaining healthy water chemistry, but how do you manage something you can’t see, touch, or smell?

You can test your water’s KH levels or buffering capacity at home using water test kits. Most strip test kits will measure KH, and these are a good option for testing general water parameters. However, liquid test kits tend to be more accurate, even if they do take a little more effort.

Start by measuring your source water, whether it comes from a tap, a well, or any other source. This will give you a good baseline reading that you can monitor over time.

Now, KH levels tend to decrease over time as acids are released into the water, so you’re going to need to test regularly to find out how long you can go between water changes or treatments. Once a week is a good schedule if you’re starting out with naturally low KH levels.

Suggested Carbonate Hardness

So now that you know what carbonate hardness (KH) is and how to measure it, you’re probably wondering what your levels should be in your tank water. The answer depends on which kind of fish you keep, so keep reading to learn about suggested levels for specific fish types.

• African Cichlid Tank: about 200 – 400 ppm/ 11-22 dKH
• Discus Tank: about 50 ppm/ 0-3 dKH
• Planted Tank: about 50 – 100 ppm/ 3 – 6 dKH
• Brackish Water Tank: 200 – 400 ppm/ 11 – 22 dKH
• Koi Pond: about 125 ppm/ 7 dKH
• Shrimp Tank: 18 ppm or 1 dKH for Caridina shrimp. 54 – 180 ppm/ 3 – 10 dKH for Neocaridina
• Typically Community Tank: 70 – 140 ppm/ 4 – 8 dKH
• Saltwater Tank: 140 – 2000 ppm/ 8-12 dKH

Author Note: KH is described either as parts per million (PPM) or degrees (dKH/°KH), and one degree is roughly equivalent to 18 ppm.

The figures mentioned above are good general guidelines, but you should definitely research the preferred KH range of each fish species you keep to make sure you can provide a healthy tank environment. Remember, each fish in a community setup should be comfortable in the same tank.

How To Adjust Levels

Sometimes you need to adjust your KH to keep certain fish species or to increase your tank’s ‘safety net’ against pH swings. Continue reading to learn how.

How to increase carbonate hardness

Water Changes

Carbonate hardness naturally decreases over time as acids are neutralized and carbon escapes the tank in the form of carbon dioxide. Performing regular water changes and sucking up decaying organic matter from the substrate will remove acidic nitrates from your water.

Topping up your tank also reintroduces carbonate and bicarbonate ions to increase your KH levels. However, water changes are not going to increase your carbonate hardness above your source water’s (tap, well, etc.) natural KH level.

So how do you increase KH above the levels of your source water? Continue reading to learn about five things you can add to the water to increase your KH.

Alkaline Buffers

Alkaline buffers, like the range produced by Seachem, make raising and maintaining your KH levels very easy. These products provide excellent dosage instructions to make your adjustments much safer and more precise.

After regular water changes, alkaline buffers are the best option for beginners, and you might even find a product designed specifically for the type of fish you keep.

Crushed Coral

Crushed coral is mostly made up of calcium carbonate, which is great for increasing your water’s buffering capacity.

Crushed coral is my go-to recommendation for anyone who needs to raise KH in a freshwater setup. It’s inexpensive, widely available, and low-maintenance — you can mix it into your substrate or tuck a mesh bag of it into your filter’s media basket and let it work passively over time. Unlike baking soda or liquid buffers, it releases slowly and won’t cause sudden swings. I’ve pointed more beginners toward crushed coral than any other KH solution over the years.

It is easy to find and easy to use, simply pick up a bag from your local pet store or order it online and mix it in with your gravel at the bottom of the tank. Alternatively, add some to your filter’s media basket in a mesh bag.

Aragonite and Dolomite Substrate

Aragonite is a natural form of calcium carbonate, which is the same mineral that makes up crushed coral. It has a fine, sand-like texture and it makes an ideal substrate for raising KH levels in African Cichlid tanks.

Great For African Cichlids

Carib Sea Aragamax Sand

Boosts pH

Aragamax is great for African setups as it keeps pH and hardness levels stable

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Dolomite is a mineral composed of calcium magnesium carbonate. It is another popular substrate that raises both the KH and general water hardness of your tank water.

These substrates provide a long-lasting effect, but you can’t remove them without completely draining and re-scaping your tank.

Baking Soda and Soda Ash

Baking soda (sodium bicarbonate) and soda ash (sodium carbonate) are easily available and highly affordable minerals that can be used to raise KH and pH in aquariums.

However, they must be used very carefully since they can cause sudden and powerful swings and may need frequent dosing to maintain stable KH levels. While they can be effective, they are not as safe or easy to use as purpose-made aquarium alkaline buffers.

How to Decrease Carbonate Hardness

Some animals, like Caridina shrimp and discus fish, need very soft water to stay healthy, so what do you do if the KH levels in your source water are too high?

It’s not practical to remove carbonate hardness from your tap water, so your best option may be to cut your high KH water with something with a lower carbonate hardness. If you want to go really low, you may need to switch to a completely different water supply.

Here’s the honest advice I give every beginner dealing with high KH source water: the path of least resistance is almost always choosing fish that prefer those parameters rather than fighting to lower them. African cichlids, guppies, and mollies thrive in hard, high-KH water — and they’re genuinely beautiful, interesting fish. Going to great lengths with RO systems and buffers to chase low-KH conditions for discus or Caridina shrimp is a rewarding challenge when you get it right, but it’s genuinely hard to maintain consistently. Know your source water first, then choose your fish accordingly.

Let’s take a look at some of the best options.

Reverse osmosis water

Reverse osmosis (RO) is a process that removes minerals from water by passing it through a membrane, leaving it with practically no carbonate hardness. It is safe for use in aquariums, but only if you add essential minerals to the water using products like Seachem equilibrium and Alkaline Buffers.

My Pick

Seachem Equilibrium

A great remineralizer for freshwater tanks. Best used with RO, RODI, and distilled water. Completely aquarium safe

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You can also mix RO water with your regular source water to reduce your KH levels, although you’ll need to use your test kit to work out the correct ratio for the type of fish you keep. A 50/50 mix of this pure water and your regular water will halve the KH and GH of your tank water.

Reverse osmosis is often available for sale as drinking water, but using this in your aquarium will become expensive, especially if you have many fish tanks. RO filtration systems have become more affordable and easier to source, so it might make more economic sense to set up your own dedicated system in the long run.

Distilled Water

Distilled water has similar properties to reverse osmosis water but the purification method differs. This water is purified by boiling and collecting the evaporated H2O molecules.

Pure distilled water contains none of the minerals that fish and aquatic plants need for healthy biological functions, so you should not use it without adding minerals or mixing it with tap or well water.

Buying distilled water is a good option for small freshwater tanks, but it will get expensive for larger aquariums.

Organic Matter

You can also decrease your KH levels a little by adding aquasoils, driftwood, and peat moss to your tank, although the effect may last just a few weeks or months.

Reducing the frequency of water changes is another possible option, but you will need to monitor your nitrate levels carefully to prevent any health issues in sensitive fish species.

Acid Buffers

You can also lower the KH levels in your water using purpose-made aquarium products. Acid buffers convert KH into carbon dioxide, which can be great for freshwater aquariums with live aquatic plants.

FAQs

Final Thoughts

KH is an important water parameter that all aquarists should understand, especially when keeping sensitive fish or species with very specific pH requirements. Fortunately, you don’t have to be a qualified chemist to understand the basics of aquarium water chemistry.

A good quality water test kit and half an hour each week for a quick water change is usually all you need. However, there’s also a range of excellent products available to the modern hobbyist that can make managing high or low aquarium KH levels really easy.

How do you manage the KH levels in your aquarium? Let us know in the comments below!

🐟 Want to learn more? This article is part of our complete Aquarium Care Guide — your ultimate resource for water chemistry, maintenance, feeding, disease prevention, and everything you need for a healthy tank.