Cloudy Fish Tank – 7 Common Reasons (and How To Fix 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 water. I get your pain, as I have been in the hobby for over 25 years. While the problem is not as common on the saltwater tank side, it is far more common for freshwater tanks.

There are several reasons for cloudy water in freshwater tanks. 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.

Key Takeaways

  • The most common reason for a tank that is murky or water cloudy is having a new tank
  • Proper maintenance and stocking are good ways to prevent a tank from becoming cloudy
  • If your tank needs to be cycled, consider bacteria in bottle products
  • Glass can also make your tank look hazy, clean the inside and outside of your glass

Why Is My Fish Tank Cloudy? The 7 Most Common Reasons for Cloudy Water

Murky 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

Check out our video from our YouTube channel below. We go into more detail in the blog post. Free to follow along with both.

1. New Aquarium and Murky Water

Cloudy water in a fish aquarium and a new tank go hand in hand with 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 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 reproduce like crazy in order to digest the excess nutrients. The massive amounts of new bacteria create a cloud, which results in your water looking cloudy. The best way to fix cloudy water issues 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 do a water test 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

If you have an established tank, this is a common reason for tank water in your aquarium to become cloudy. 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 dirty aquarium water. The only fish you don’t want to do this with would be fish that 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 in the tank is going to lead to a dirty-looking aquarium. Adding them too fast will also cause the water in the tank to look clouded. Slow yourself down with additions and avoid adding any more fish until you get this problem under control.

When planning out fish, a really great site to get an 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 of this problem in an established 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 it to fit.

5. Dead Fish Or Matter

Decaying matter can cause murky water in your tank and will get dirty 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 is dirtying up your tank water.

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

6. Your Glass

Your glass can be a source making your tank water look murky. 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 cloudiness or milky water that will look hazy if they are not rinsed. Always make sure you wash your substrate thoroughly 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 causing it to look milky. 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 It

Alright, so we know the 7 common causes of cloudy aquarium water. Let’s talk about what we can do about it. It’s actually simpler than you think and here are 5 ways to get rid of it:

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

1. Proper Aquarium Maintenance

Dirty Fish Tank

Proper maintenance on your tank is going to be the #1 solution for white 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 and balance the water chemistry. In most cases, clouded 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 change every day or every other day is not uncommon when dealing with a serious nutrient spike that causes a tank to become dirty. Gravel vac your substrate. If you have a fine substrate, surface skims 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 hazy 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!

Click For Best Price Buy On Amazon

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 dirty tank water problems. 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 tank, cycling your aquarium is your first step to avoiding  having a brown water tank. Reduce your feeding and don’t add any more 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 have a newer tank is getting used filter media from a disease-free tank. This will import 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

Buy On Amazon Click For Best Price

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 mitigation. 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 and water clear.

Common Questions (FAQS)

Why Is My Aquarium this way?

A tank can get dirty or look clouded 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 Dirty Water Bad For Fish?

The appearance of clear 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 hazy water would be to assess your water quality by testing your aquarium water. Get a baseline of your nutrient levels and take action as needed. 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 maintenance schedule, and keeping your stock levels stable are the best ways of making your aquarium water crystal clear. You can also purchase equipment and supplies that can assist greatly like an aquarium UV sterilizer.

Will A Filter Clear Hazy Water?

A filter can fix cloudy aquarium 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 water that looks cloudy or hazy. Other times, the filter is the problem because it’s dirty and needs to be maintained.

Can Driftwood Make My Aquarium Murky?

Driftwood can make a tank look cloudy or murky. 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

Implementing a proper aquarium care routine will help to avoid cloudy water tanks. Various types of fish that can also make the water cloudy such as Yellowfish and tropical fish, so you have to make a regular cleaning schedule to maintain your aquarium. Tropical fish also require specific water and temperature conditions, or they will get sick. Sand and other equipment can also affect the water in your aquarium when not properly cleaned.

Have you dealt with dirty 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!


  1. Really glad I was guided to you when I asked Google about my cloudy tanks. I am going to change the water in my tanks. clean my filters again and buy new filters and a vacuum. Question…I am nervous about using tap water because of any additives in it. Would it be fine or should I use bottled water or large amounts that has sat for 48 hours. Mahalo for your time and knowledge Ellen

    • Hi Ellen. Bottled water could work. I would suggest getting a TDS meter to double-check. If the TDS is too low, it could be a problem for water changes. Generally, for freshwater community fish, 100-300 is your target. If it’s less than that, you will want to add a mineral product

    • 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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