Fish Tank Yellow Water: Causes, Prevention, and More!

Last Updated on January 10, 2022

After a week of long day’s work, going home and watching your colorful fish swim around is a nice way to relax. Then suddenly, you start noticing that your tank water is cloudier than usual.

Do you know the feeling of seeing your fish tank and being alarmed by its color? There is nothing more stressful than seeing your tank water turning yellow or brown! This can be a huge headache since all you want for your fish is a beautiful aquarium they can enjoy.

This post will help guide you through what might be causing that nasty yellow tank, how to fix it, and some great tips for keeping your fish happy for a long time!

fish tank yellow water

Why is my tank water yellow or brown?

Usually, tank water is supposed to be clear and without color. If your water turns yellow or brown, most likely there is something wrong with your fish tank.

If you are wondering why your tank has cloudy water, here are some possible reasons you may want to look into.

Bacteria growth

Most probably, the root cause of why your water is cloudy is due to bacterial growth. It is not a secret that your fish tank is full of bacteria – both healthy and not – that could affect the color of your tank water.

When your aquarium is exposed to certain bacterias, an overgrowth that is sometimes referred to as the bacteria bloom will surely form inside your fish tank. When this happens, the bacteria will make your water seem cloudy or yellow-looking.

A microorganism can sometimes affect the color of your tank water, making the water turn yellow because of the abundance of algae and waste. Although algae are green, they could eventually change their shade to yellow or gray when exposed to the water for a long period of time.

If you notice that your fish tank is already getting cloudy and gray, don’t just brush it off and expect the algae to go away on its own. Get rid of it and keep your fish healthy and happy!

Driftwood tannins

Not all water discoloration is something to be worried about. Sometimes, dealing with the yellow aquarium water is simply just because of driftwood tannins and even other plant materials.

Woods like driftwood and bogwood contain tannins which could change the color of the tank water over time. Having a yellow or brown tint, tannins are acidic in nature and may disrupt the pH level in the fish tank.

If you have a fish that can thrive in a low pH level of water, then there is nothing to worry about. But best to learn about the pH preference of your fish before putting them inside their tank.

Tannins usually go away on their own and so does the yellow water. You may even be surprised to see that some species of fish enjoy being in yellowish or brownish water as it looks closer to their natural habitat.

Organic compounds

Dissolved organic products such as fish waste, decaying dead plants, and uneaten food are just some examples of organic compounds that can change the water’s chemistry and ammonia level.

As a result, this dissolves in the water and turns it into a more yellow, green, or brown tint. Moreover, dissolved organic compounds could also turn the water cloudy and murky which is very harmful to your fish’s health – causing death if not treated immediately.  

Again, there are many reasons to consider here. Fish waste for example creates a heavy bioload in your tank which can eventually affect the water quality if you don’t have any filter.

Dead or rotting materials floating around is another thing to watch out for. Rotten plants, uneaten food, and even a dead fish that you weren’t able to scoop out may be the culprit.

Affecting your tank’s overall aesthetic, organic compounds will only not make your fish tank look messy but can also lead to unpleasant odors. Getting rid of this problem should be done sooner than later when you start noticing discoloration and unpleasant smells rising from your tank.

Tap water

Are you using tap water as your main aquarium water? If yes, then this could be the reason for your fish tank to turn yellow. 

In some regions, tap water contains too much iron and manganese. Although safe to consume and bathe in, this may leave a yellow tinge in your water. Don’t worry though! You can solve this problem by using Reverse Osmosis water.

There are stores out there that sell RO water. But if you prefer to save money and own one, then you can also choose to buy your own RO unit!

Dirty substrate

New tanks are surely prone to water issues. 

After setting up your aquarium, you may have noticed that your water is turning murky and yellow. If this is the case, then most probably this is due to an unwashed substrate like gravel. 

Substrates have dust and contaminants on them that is why it’s very important to wash them first before putting them inside your fish tank. Once you’ve washed it, then your aquarium won’t turn yellow unless your substrate contains tannins.

Although not harmful and contaminating, it’s best to rinse and clean your substrate first so you can keep your aquarium water clean and safe for your fish!


Who would have thought that even lights could discolor your aquarium water? 

While the light doesn’t directly cause your discolored and cloudy water, the lighting period however could be responsible for bacteria production.

If you start noticing green algae production and bacteria bloom in your fish tank, you may want to cut back the duration of your lighting period. 

As discussed earlier, an overgrowth in bacteria will affect the clarity and color of your aquarium.

Why clean water matters for your fish?

When was the last time you cleaned your tank? Although washing your tank is a dirty job, there are many reasons why you should do it, and here are just a few.


The dirtier your tank is the more bacteria, fungus, viruses, and threats there are to your fish. This could also lead to an unbalanced pH which will make the environment less safe for your pets.


Is there floating debris and excess waste in your fish tank? When a fish tank is filled with these floating wastes, it could clog your filter, pump, and other equipment essential in keeping your aquarium clean. 

In worse case scenarios, it could even destroy your equipment which will leave the tank’s environment dangerous and deadly for your beloved fish.


Looking at yellow, dirty water is surely not enjoyable especially if your fish tank will be filled with slimes and algae.

When this happens, it will be very difficult to see your colorful plants and fish. On top of that, a dirty tank may even put off unpleasant and foul odors.

How can I improve the quality of my aquarium water?

If you have a fish aquarium at home, you might be wondering how to keep your water clean. It’s important to take care of the water quality in your tank for the health and well-being of your fish. The good news is that there are plenty of ways to maintain excellent aquarium water quality!

Check the conditions of your water

Before making any changes to your aquarium water, you may want to test your water first. Checking the conditions of your water will help you figure out what could be causing your yellow aquarium water.

The first thing to check is the nitrite, nitrate, ammonia, and pH levels. Once you’ve measured this, this will help you determine if you have a waste problem in your aquarium. If you do have, then it is time to fix your water chemistry with a partial or full water change, depending on how dirty your tank is.

Moreover, check if your water has any floating debris as this could also cause your water to turn yellow or brown. Look for any dead plants, old food, or any other particles floating around, and make sure that you haven’t left any object that could rot in your tank!

Related: What is the Best Water Conditioner for Betta Fish?

Get a filter

Another thing you can do as maintenance is to invest in a tank filter. If you already have one, make sure that it’s working just fine. Also, you may want to make sure that your filter is suitable for your tank size since incompatibility will also cause water problems. 

Water quality issues should be lessened with the help of filters as they will keep your water clear. Usually, bacteria bloom and contaminant buildup happens when you don’t have a filter in your aquarium.

When water turns yellow or brown, check on your filter to see if it’s working properly. Change the cartridge if needed and routinely as this gets dirty over time. When doing this, ensure that you remove any clogging in your filters then get them taken care of quickly before they start making things even worse than they already are! 

Wash wood and substrate

Driftwood and gravel should be rinsed off first to remove any excess tannins and dirt. Although not necessarily toxic, not everyone likes it when their tank has cloudy water.

Removing tannins from the wood and other substrates will help make your water clearer. If you already rinsed it and it still discolors your aquarium, you can try soaking all the tannins out in a bowl until you get rid of it all.

To do this, all you have to do is prepare a bowl with warm water and leave your driftwood in it. After 24 hours, the tannins should be all gone by then – making your water less likely to turn yellow or brown in the process!

Perform a water change

Water changes should help clear up your water effectively. For best results, it is recommended to have a 40 percent water change to help bring the concentration of toxins down.

Keep in mind to do this process carefully so as not to stress out your fish with the sudden change. Your fish is surely stressed out with their dirty aquarium environment and drastically doing a water change will cause them distress more.

Always make sure that the new conditions you are preparing your fish for are suited for their needs and well-being.

Related: How Often Should You Change Betta Fish Water

Remove decaying materials

Leftover fish food, decaying plants, dead fish, and floating debris are just some of the decaying materials you should remove immediately. Doing a water change is not enough if you won’t take out rotting organic materials which will just infect your new water and turn your water cloudy and brown again.

When performing a water change, remember to also remove anything that is rotting or could rot!

Always do tank maintenance

If you really want to avoid having a dirty aquarium, you have to make a habit of cleaning it up regularly – at least doing a thorough cleaning every month.

There are many tools and devices especially made to help maintain the water quality of aquariums. One device you should invest in is the gravel vacuum which quickly sucks up waste at the bottom of the tank. This device is also very helpful when doing a water change.

While water changes can be annoying at times, this still has to be done every week or two, depending on your tank’s size and water quality. Another thing to consider is removing growing green algae with a razor or scrubber when bacteria bloom starts becoming a problem.

Related: How to Keep a Betta Fish Tank Clean: Step by Step Guide

Final thoughts

Fish are important creatures that deserve a healthy and clean home, so it’s up to you now to make sure that their tank is taken care of properly! 

Know and get rid of the things that can pollute your tank water and take these steps when cleaning or maintaining your aquarium in order to keep the water clear, fresh, and free from pollutants. 

Remember that the last thing we want for our pet fish is dirty water. We recommend consulting with an expert before making any drastic changes in your tank but we hope these tips will get you started on improving your pet’s home. 

Now go care for your fish so they have a happy home!