Cloudy Fish Tank – 7 Common Reasons (and 5 Ways To Deal With It!)

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Dealing with a cloudy fish tank? If you have dealt with this, you will know it is one of the most frustrating things that can happen in the fish tank hobby. I get your pain, as I have been in the hobby for over 25 years. While the problem is not as common in the saltwater tank side, it is far more common for fresh water tanks.

Freshwater tanks deal with cloudy tanks for a variety of reasons. In today’s post, I’m going to go through the 7 most common reasons for a cloudy fish tank, and 5 ways you can go about resolving the issue. Knowledge is power in this hobby and I’m here to empower you! Let’s get started.

The 7 Most Common Reasons Why You Have A Cloudy Fish Tank

Cloudy water sucks. It makes your tank look ugly and unappealing. Fortunately, there are 7 common reasons for it occurring, they are:

  1. You Have A New Tank
  2. You Are Overfeeding Your Fish
  3. You Have Too Many Fish
  4. You Don’t Have Adequate Filtration
  5. There Is A Dead Fish Or Decaying Matter
  6. Your Glass
  7. Your Substrate

1. New Tanks and Cloudy Water

Cloudy water and a new fish tank go hand in hand our hobby. It is very common for this to happen when you are cycling a tank or have a newly cycled tank. When you start adding livestock to the fish tank, you introduce new sources of nutrients and waste to the tank. If you add too fast, the system is thrown off balance.

As a result of this imbalance, the beneficial nitrifying bacteria in your tank reproduces like crazy in order to digest the excess nutrients. The massive amounts of new bacteria creates a cloud, which results in your cloudy water. The best way to resolve this issue is patience. Just stop adding fish and let your tank settle down. It should clear up on its own.

During this time, it is a good choice to test your aquarium water with an aquarium test kit. You will want to look at the big three new tank parameters, which are going to be Ammonia, Nitrite, and Nitrate. Ammonia and nitrite are going to be your biggest concerns with a brand new tank.

2. Overfeeding Fish

If you have an established tank, this is a common reason for cloudy fish tank water. It’s understandable to want to feed your fish all the time. After all, they usually greet you when they see you with their cute little faces. They look at you, and the top of the tank waiting for you to feed them. If you start feeding a lot, your system gets thrown off balance and a bacteria bloom occurs.

Lay off the feeding for a bit and test your aquarium water. It’s actually a good thing to have your fish go without food for a day to let their digestive systems settle down. Excess food is problematic and can lead to cloudy aquarium water. The only fish you don’t want to do this with would be fish who lack stomachs, like goldfish. Look out for automatic fish feeders as it is easy to overfeed with them.

3. Too Many Fish

Too many fish is going to lead to a dirty looking and cloudy fish tank. Adding them too fast will also cause cloudy water. Slow yourself down with additions. If you have cloudy water, avoid adding any more fish until you get it under control.

When planning out fish, a really great site to get a overview is AdAdvisor. Just plug in the fish you want to add and run the calculator. As a rule of thumb, you do not want to increase your fish population by 50% and you want to spread out your additions to 4-6 week timelines so your tank has time to balance out. The only time I feel where you can get away from this is if you have done a dry start for a planted aquascape. Here is the link to the calculator.

4. Inadequate Filtration

Filtration is a major cause for cloudy water in an established fish tank. The main culprit here is going to be your mechanical filtration. Cheaper power filters tend to use coarse foam, which finer particles will pass through. When it comes to canister filters, the issue may be the choice of foam. Fortunately, high end brands like the Biomaster Thermo will have multiple foam densities you can choose from. If you have a heavily populated tank, you might want to consider going for a finer foam.

If you are using a power filter, you might want to consider adding a layer of filter to improve your mechanical filtration. I prefer to use the blue floss that is put in canister filters and sumps. You can purchase it in bulk online and then cut to fit.

5. Dead Fish Or Matter

Decaying matter can cause your aquarium water to get cloudy fast. The biggest piece of decaying matter is going to come from a dead fish. Check your tank every day and see if all the fish you own are accounted for. Sometimes, if your fish are breeding, you may have dead fry that are dirtying up your tank water.

The other factor is going to be chucks of uneaten fish food and decaying plant matter. Check your substrate for both and trim of any decaying leaves you see on your live plants.

6. Your Glass

Your glass can be a source making your tank water look cloudy. The main cause is from bacterial biofilm. Biofilm looks the most obvious on aquarium driftwood like in the photo below, but it also grows on your glass.

Biofilm In Aquariums

This biofilm will stick to your glass and give it a cloudy look if left unchecked. On larger fish tanks, your tank will have a slight tint to it that will make it look a little darker. Low iron rimless aquariums and acrylic tanks will have better clarity and show better than traditional glass tanks.

7. Your Subtrate

New substrates can cause cloudy water if they are not rinsed. Always make sure you wash your substrate throughly before putting it in your aquarium. The other cause can be an existing substrate that is stirred up. Stirring up too much of your substrate at once can cause the release of additional nutrients, which will cause a bacterial bloom or cause discoloration of your aquarium water. If you are going to stir your substrate, it is best to do so when gravel vacuuming so you get most of the debris that comes out

5 Ways To Deal with Cloudy Aquarium Water

Alright, so we know the 7 common causes of cloudy aquarium water. Lets talk about what we can do about it. Its actually simplier than you think. There are 5 ways to get rid of cloudy water, they are:

  • Proper Fish Tank Maintenance
  • Making Sure Your Glass Is Clean
  • Proper Filtration Maintenance
  • Cyling Your Aquarium
  • Improving Quality Of Light Duration

1. Proper Fish Tank Maintenance

Dirty Fish Tank

Proper maintenance on your fish tank is going to be the #1 solution for cloudy aquarium water. Most problems in this hobby can be resolved with a water change. A water change can bring balance back into your aquarium. In most cases, cloudy water is going to be a result of a bacterial bloom due to spikes in nutrients. Doing a water change will remove these nutrients and get everything in balance. If the problem is more serious, you will need to do more water changes over time to get everything back to where it should be.

In extreme cases, 40-50% water changes every day or every other day is not uncommon when dealing with a serious nutrient spike that causes a cloudy fish tank. Gravel vac your substrate. If you have a fine substrate, surface skim it with the gravel vac to remove the top layer of debris.

2. Making Sure Your Glass Is Clean

Both the outside and inside of your glass matter. Outside of the tank, water stains on the glass can make your tank look like there is cloudy water when trying to look in. Work with a safe cleaner, like white vinegar, or better yet, use a DIYers secret weapon – Magic Erasers!

Yes, that’s correct. The original Magic Eraser by Mr. Clean has been a blessing for acrylic aquarium owners for many years and goes unnoticed in our hobby. I’ve used it on the outside of the glass with great results. Rumor has it that it works inside the tank as well, but I’m not that brave ?. Still, I’ve had hobby friends tell me that it’s like cleaning with a plastic scraper and is completely safe. I’ve only had personal experience on the outside. For the inside, I prefer a razor blade for glass or a Flipper Cleaner.

My Pick
Flipper Algae Scraper

I love the Flipper. Just put it in your aquarium and clean from the outside. You can even move it to other sides of the tank with its flipper feature. Simply Amazing!

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The Flipper is amazing for cleaning the inside of your tank. It’s been my go to for years. It is also a great way to get your kids involved, as they can clean from the outside without having to put their tanks in the tank. There is also a cool factor with flipper the scraper when you move it to the other sides of the tank. It will scrape off the toughest of algae from your glass and make your glass look spotless!

3. Proper filtration maintenance

If you slack on filter maintenance, this can lead to cloudy fish tank water. Your mechanical filtration is not operating at its maximum efficiency. Get into those filters and replace your filter floss and wash out your sponges. You should be changing out your filter floss every other week. For all the filter media you clean, make sure you clean them out with your tank water. If you use tap water or RO water, you risk losing those beneficial bacterial colonies in the process.

Clean out the piping in your power filters and the tubing in your canister filters. If you have mechanical filtration, consider replacing it for a fresh set. Sometimes upgrading to a premium chemical filtration media like chemi-pure will help, though it is expensive to do. All this maintenance pays off because your filters will operate at their best, keeping your tank water looking crystal clear.

4. Cycling Your Aquarium

If you have a new fish tank, cycling your aquarium is going to be your first step with combating cloudy water. Reduce your feeding and don’t add anymore fish until the problem goes away. Test your water for ammonia and nitrite levels and do a water change to reduce the excessive nutrients.

Another thing you can consider if you are have a newer tank is getting used filter media from a disease free tank. This will import over beneficial bacteria that will jump start the cycle. You can also opt for using beneficial bacteria in a bottle solutions like Fritz Turbo Start 700.

My Pick For Freshwater Bacteria
Fritz Turbo Start 700 Freshwater

Fritz Turbo Start is known in the industry as the fastest acting nitrifying bacteria you can purchase. This 700 version is specialized for freshwater tank and has my highest recommendation

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If you are looking for a longer term solution, a UV Sterilizer is a great addition for not only water clarity purposes, but also for disease migration. Check out my article on Aquarium UV Steriliziers for more information on what makes a good one. There are many out there, and only a few that I would recommend.

5. Improve quality of light and Reduce Lighting Times

Poor lighting can really dull out your aquarium and give it a hazy look. This is more common with LED lighting as the light is more focused than T5 lights. Because the light is focused, it can lead to a disco effect and shadows can dull out your tank. I prefer an LED fixture that expands to the length of the entire tank like the Twin Star or Fluval planted tank led.

If you have T5s, it may be time to replace the bulbs. Getting new bulbs will brighten up the aquarium and make it look more lively and clearer. T5s in general also tend to display a clearer tank, given their even spread of their light. You can get close to this with LEDs, but only with higher end LEDs, like the ones I mentioned previously.

Reducing your lighting time can also help. This will slow down the reproduction of algae which will keep your glass clear.

Common Questions (FAQS)

Why Is My Fish Tank Cloudy?

A fish tank can get cloudy for one of the 7 common reasons. You have a new tank, you are overfeeding you are overfeeding your fish, your tank is overstocked, you do not have enough filtration, there is a dead fish or decaying matter in the tank, your glass needs to be cleaned, or you have put in new substrate.

Is Cloudy Water Bad For Fish?

The appearance of cloudy aquarium water is not bad for a fish, but is a sign of imbalance and possibly a greater problem. The first thing you should do when you see cloudy water would be to asses your water quality but testing your aquarium water. Get a baseline of your nutrient levels and take action as need. Usually a water change will help put things back in balance.

How Do I Make My Aquarium Water Crystal Clear?

Great filtration, a good aquarium maintenane schedule, and keeping your stock levels stable are the best ways of making your aquarium water cystal clear. You can also purchase equipment that can assist greatly like an aquarium UV sterilizer.

Will A Filter Clear Cloudy Water?

A filter can clear cloudy water. If your tank is new, your filtration system needs to catch up to balance your tank. If you have a heavily stocked tank, you may lack filtration and may need another filter to alleviate the cloudy water. Other times, the filter is the problem because it’s dirty and needs to be maintained.

Can Driftwood Make My Tank Cloudy

Driftwood can make a tank cloudy. However, the most common issue with driftwood is it can turn your aquarium water a tea like color due to the release of tannins. Some aquarium owners like this look, I personally don’t. If you want to avoid that tea color, purchase a driftwood with a low tannin count like Manzanita or Tigerwood

Conclusion – Share Your Experiences

Have you dealt with cloudy water before? How did you clear it up? Share your experiences below and let’s start a conversation! I hope you found this article helpful. I also love to hear from my readers. We have all dealt with this before and we can work together as a community to help others. Thanks for reading and see you next time!

by Mark

Mark is the founder of Aquarium Store Depot. He started in the aquarium hobby at the age of 11 and along the way worked at local fish stores. He has kept freshwater tanks, ponds, and reef tanks for over 25 years. His site was created to share his knowledge and unique teaching style on a larger scale. He has worked on making aquarium and pond keeping approachable. Mark has been featured in two books about aquarium keeping - both best sellers on Amazon. Each year, he continues to help his readers and clients with knowledge, professional builds, and troubleshooting.


    • Hi Frank,

      It depends on your budget and setup. If you are looking for effective and value, go with the Aquaclear hang-on filter. If you have a planted tank and desire very clean water, go with the OASE canister filter. Those are the two filtration units I recommend to everyone. You can see my articles on hang-on filters and canister filters here and here.


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