7 Reasons Your Aquarium Water Is Turning Yellow

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Last Updated on 2023-08-08

When you have a fish tank, one of the things you want is for the water to be very clear so you can watch your fish swim around. Most of the time, aquarium water is clear and has no color, but sometimes it can get cloudy and turn yellow. This is usually a sign of trouble, but there can be times when it isn’t. When the water starts to turn yellow, you should find out why as soon as you can so you can fix anything that needs to be fixed. This article will talk about yellow aquarium water, including what causes it and how to fix it.

Why Has Your Aquarium Water Turned Yellow?

Yellow water in an aquarium is not nice to look at and may not be good for your fish to swim in. This is something almost every experienced aquarium hobbyist has seen more than once. This can happen for many reasons, and here are seven of them.

1. Algae Bloom in the Water

If your aquarium has turned yellow, it might be because of algae. Algae can make the water look yellow and make it unsafe for your fish to swim in because they can use up all the oxygen in the water, making the fish suffocate. Algae are usually green in color, but when they are in the water, they can sometimes look yellowish.

2. Tannins

One common reason for discolored water is the presence of tannins. Driftwood contains tannins, which will eventually seep into the water and turn the water a murky yellow to brown. The tannins in the water will soften it and reduce its pH, which could be desirable and even recommended for certain fish species.

3. Fish Waste

The fish can produce waste products in the form of poop, which contaminates the tank. When fish waste is left in the tank for longer than it should be, it can change the color of the water and make your fish sick. Cleaning your tank on a regular basis and installing a water filter will remove any substances that may be causing the water in your fish tank to turn into yellow.

4. Rotting Plants 

Brown or yellow water in a fish tank can also come from plants that are dying. As the plants die, they change the color of the water in the aquarium to yellow or brown. They also increase the amount of nitrates in the tank, which makes things worse for your fish. When this happens, it can throw off the water’s balance, which can lead to more problems.

5. Unwashed Substrate

Just putting substrate in your tank without washing it can change the color of the water. Sometimes tannins may also be found in some substrates, which can also cause the water to turn yellow. Your substrate may not be polluted or harmful, but it’s still a good idea to wash it so you can keep your aquarium clean and safe.

6. Leftover Fish Food

Yellowish water is sometimes caused by dissolved organic compounds from extra fish food that the fish didn’t eat. If you feed your fish too much, it can also hurt its health and digestive system in other ways. To keep this from happening, make sure to feed your fish the right amount of food at the right times.

7. Too Many Fish

If fish and plants are overstocked without proper maintenance, the water could turn yellow and lead to a chemical imbalance. This can make your fish and plants sick, and it can sometimes kill them. To stop this from happening, make sure your aquarium has the right number of fish and plants and is cleaned regularly.

How Do You Fix Discolored Aquarium Water?

People don’t like to look at fish swimming in dirty water, and it’s not good for the fish either. Aquarium water usually turns different colors, and it’s completely normal, but that doesn’t mean you should just leave it that way. The good news is that you can make your water clear again by taking some simple steps. Here are some of them.

1. Change The Water Regularly

If there is too much food and fish waste in your tank, you should get rid of it because it could be the reason why the water in your tank is discolored. Try to replace about a quarter of the water every 2 weeks, and make sure to do it slowly to avoid shocking your fish. You can also use a vacuum for the aquarium and clean the gravel or substrate while doing a water change.

2. Install a Water Filter

If your tank doesn’t have a filter, waste and other contaminants will quickly fill up in your aquarium. Also, the water quality will be bad if you use a filter that isn’t made for the size of your tank. Make sure you put in a water filter that is the right size for your aquarium so that the water doesn’t get discolored.

3. Get Rid of Dead Plants

If you don’t get rid of the decaying plants in your tank, the new water you put in when you change the water will get infected and get discolored. This could also be rotting plant leaves or roots that could probably be hard to find, especially if you have lots of plants. After you take it out, give your tank a light cleaning and wait a few days to see if the color change stays.

4. Get Rid of Tannins

You can get rid of tannins and discolored water in your fish tank by using activated carbon. Activated carbon is made of granules of charcoal that have been treated with heat and chemicals. This increases their reactivity and their ability to absorb tannins and other compounds that could be harmful to your fish.

5. Get Rid of Dead Animals

If you have a lot of fish or snails in your aquarium, the discolored water could be caused by a dead fish hiding behind your plants. These can go unnoticed for days, rotting and decaying, which could turn the water in your aquarium yellow. Make sure there are no dead animals in your aquarium or on your plants.

6. Clean the Water Filter

There might be a lot of organic matter that has been broken down and is floating around in your aquarium, and this could be because of your aquarium filter. An aquarium filter cleans the discolored water in your aquarium by getting rid of all the floating decaying organic matter. If the filter isn’t doing its job, it’s probably clogged with debris, which can sometimes be the source of floating organic matter in your aquarium.

 7. Vacuum the Substrate

The substrate may be to blame for the discolored water in your aquarium. New aquarium substrates can contaminate the water with debris and other unwanted materials if it is not cleaned first. A gravel vacuum or siphon can be used to remove any debris or excess gravel from the substrate, which may be the source of the discoloration in the water.

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How To Remove Tannins From Aquarium Water

The water in your aquarium may turn a less-than-desirable shade of brown or yellow at some point during your fishkeeping adventures, which is completely natural but still likely to cause you some anxiety. One of many contributing factors is tannins. In this list, we will go over seven methods for removing tannins from your aquarium.

1. Activated Carbon

Activated carbon may be the most well-known material used to filter tannins in aquarium water. It is created from anything with carbon in it, like coal or coconut. It is then treated with chemicals to make it better at absorbing and holding tannins and other compounds that could be present in the water.

2. Boil The Driftwood

If your aquarium water has turned yellow, the biggest reason could be the driftwood in your aquarium. Many types of driftwood release a lot of tannins that could discolor the water in your aquarium. To stop this from happening, boil your driftwood for approximately 1 hour and 30 minutes, then dry it for at least a day before adding it to the tank.

3. Soak The Driftwood

If you don’t want to boil your beautiful driftwood, you can soak it in water to get the tannins out. Place your driftwood in a different aquarium and let it sit for a few hours or until the water in the aquarium changes color. Once the water has completely turned brown or yellow, you can do this process again and again until the water is clear.

4. Baking Soda 

Removing tannins with baking soda is a quick and easy way to get rid of tannins and keep your aquarium water clear. However, adding baking soda to your aquarium water raises the ph level of the water. To avoid harming your fish, you should transfer them to a new tank before adding baking soda.

5. Reverse Osmosis Filter

Installing a reverse osmosis filter on your water supply is another option for reducing tannin levels in your aquarium. Water purification by reverse osmosis allows only water molecules to pass through the membrane, ensuring that you will always have pristine clear water in your aquarium. This means that any unwanted compounds present in the water, like tannins, won’t make it through the system.

6. Ion Exchange Resins

Adding ion exchange resins to your aquarium is another option for removing tannins. These resins efficiently remove harmful compounds and tannins that are present in the aquarium water by attracting charged compounds and exchanging them with safer ones. The resin can also attract ammonia and nitrite, and some kinds of ion exchange resin can even remove dissolved organics.

7. Water Change

The most obvious way to get tannins out of the water in your aquarium is to change the water. Most aquarists would recommend weekly water changes of 10-15% for small tanks and 20% for larger ones. Be careful not to do it too much because it can throw off the balance of the water and cause more problems.

How to Keep Aquarium Water From Turning Yellow When You Add Wood Decorations

Driftwood is a popular aquascaping material that aquarists have been using since the beginning of fishkeeping to make beautiful, natural aquascapes in their aquariums. But no matter how pretty they are, they are known for putting tannins into the water. Here are three things you can do to make sure that doesn’t happen.

1. Soak Your Driftwood in Water

Soaking your driftwood is important for a number of reasons, but perhaps the most crucial is making it waterlogged so that it sinks. Soaking your driftwood for weeks can also help get rid of the tannins and release it into the water before you put it in your aquarium. To make sure the driftwood is fully submerged, press down on it with something heavy.

2. Boil Your Driftwood

Boiling driftwood for 1 to 2 hours, depending on its size, makes it completely clean and ready to use in the aquarium. The heat from the boiling water can help the driftwood release the tannins and other compounds. Just make sure that you rinse it and let it dry for a day before putting it into your aquarium.

3. Wash Your Driftwood

Mix one part bleach with nine parts water and pour it into a large container until it’s enough to cover your driftwood completely. Put your driftwood into the mixture. Soak your driftwood in a disinfecting solution for three to four days, changing out the solution each day to get rid of the tannins and organic compounds in the wood

Why Did Soil Make Aquarium Water Yellow?

As an aquarist, we usually try to keep the water as clear as a crystal so that it looks nice and is good for the plants. But it’s very hard to keep a complex environment in a small glass box in balance, and problems are almost certain to happen. One of these is that soil can change the color of the water. Here are seven ways that soil can turn the water in your aquarium yellow.

1. Tannins in the Substrate

Tannins aren’t usually a problem unless you’re keeping fish that need a much higher pH. Tannins usually come from driftwood, but they can also come from soil that was put in the tank without being washed. Always check the things you want to put in your aquarium twice and wash them.

2. Ammonia

When there is too much ammonia in the soil, algae will grow, which can make the water look yellow. This can occur for several reasons, but most of the time, it is because the organic matter was left to break down in the tank’s soil. To stop this from happening, make sure your aquarium has a water filter or that you clean it out every week.

3. Dead Matter

Organic compounds from all of the dead things lying on the substrate in your aquarium can dissolve in water and change its chemical composition. These can cause your water to turn a murky yellow, add an unpleasant odor, and even harm your fish. Always make sure there are no dead things lying in the soil in your tank.

4. Yellow Algae

Yellow or mustard-colored algae is a common clinger on aquarium glass, wood, decors, and even soil. Removing these algae from the surfaces of objects will require a lot of scrubbing. You can also use an algaecide in your aquarium but make sure to evacuate your fish first.

5. Leftover Food

The food in the tank will sink into the soil and rot if the fish don’t eat it. That’s why leftover food makes tank water more nitrate- and phosphate-rich. Feeding your fish too much can cause the water to turn colors, so be careful of how much food you put in your fish tank.

6. Fish Poop

Yellowing of the water can be caused by fish waste and other organic materials that were left in the soil of the aquarium. These things can cause ammonia and nitrates to build up in the water. Make sure to get rid of the trash and organic materials in the soil by vacuuming, putting in a water filter, and changing the water every week.

7. Unwashed Soil

Tannins that are present in aquarium soil can cause the water to turn a dull brown or yellow. This occurs when dirty soil or substrate is introduced into the aquarium. Make sure to wash the soil properly before putting it into your aquarium to make sure that it’s free from tannins and other harmful substances.

What To Avoid Doing When You Have Yellow Aquarium Water

Yellow water doesn’t necessarily mean that your fish are in danger, but you don’t want to take those chances. There are things you can do with your aquarium and things you should not do. Here are five things you shouldn’t do if you have a tank with yellow water.

1. Overfeeding

Overfeeding is something that you should always avoid as an aquarist. Not only does it change the color of the water in your aquarium, but it can also cause health problems for your fish. Make sure to feed your fish the right amount of food every day.

2. Adding Unwashed Substrate

Everything in an aquarium lives in a delicate balance. Make sure that anything you put in your tank is clean and free of parasites before you do it. Avoid putting unwashed things into your aquarium, even substrate.

3. Putting Untreated Driftwood

Driftwood can look nice and do good things in your aquarium, but if you put it in there without cleaning it first, it can hurt your fish. Driftwood that hasn’t been treated can add a lot of tannins to the already yellow water in an aquarium and may carry parasite eggs. If you don’t want your aquarium to get worse, avoid putting untreated driftwood in it.

4. Don’t Overcrowd the Tank

The water in the tank can also turn yellow if it has a lot of living things in it. If you have too many fish and plants in your aquarium, the water could change color and cause an imbalance that could kill the fish. It is recommended that you avoid putting too many fish in your aquarium, especially if the water has already turned yellow.

5. Don’t Put Fish That Can’t Survive Low pH

When tannins from driftwood make the water yellow, it is usually acidic or has a low pH. Many plants and animals can adapt to changes in the water and do well, but some plants and animals are sensitive to changes in the water and may die if the pH is too low for them. Dying plants and animals in our aquariums are things many of us aquarists would want to avoid.


Is Yellow Water Good for Fish

Water that is yellow or brown in color is usually an indication of problems. A number of things can cause the water to turn from clear to yellow, which can sometimes be bad for the fish.

Does Ammonia Make Water Yellow

The presence of decaying organic matter in the water can lead to a yellowing of the water. Ammonia and nitrates in the aquarium water can rise due to decaying organic matter.

Why Is Water Lettuce Turning Aquarium Water Yellow?

The yellowing of water caused by plants could be a sign of decay or dead leaves. If the water in your aquarium is yellow, it means that rotting food, fish poop, dead plants, and other organic matter have polluted it and made it unhealthy for your fish to live in.

Why Is My Aquarium Heater Turning Water Yellow?

If the water in your aquarium turns yellow after you put in an aquarium heater, you may have raised the temperature of the water too much. Warm water makes your fish more active, so they need more oxygen. This uses up the oxygen in the water quickly or kills your fish, which can make the water turn yellow.

What to Put in A Tank to Clear up Yellow Aquarium Water After Overfeeding

If you overfed your fish and turned the water in your aquarium yellow, you can put ion exchange resins in it. This can get rid of the compounds that make the water yellow by attracting them and changing them into less dangerous compounds. The ammonia and nitrates in the water can also be attracted to these resins.

Does Driftwood Make Aquarium Water Turn Yellow?

Tannins are present in driftwood, and over time they will leach into the aquarium water, staining it yellow to brown. Tannins lower the pH of the water and soften it. For some fish, this may be desirable and even recommended.


Something is definitely wrong if the water in your fish tank has turned yellow. And this should tell you that you should probably look into the cause of the problem and fix it as soon as you can. Yellow water doesn’t always kill our fish and plants, but the thing that made it yellow might be bad for the fish, and as an aquarist, we don’t want to take any chances. We can fix this problem by installing filters, putting exchange resins in the tank, or changing the water, all of which can help eliminate the water’s yellowing. There are also things that we, as aquarists, should not do, especially if our aquarium water has already turned dirty and yellow. A yellow aquarium is not the best thing to keep around if you want your fish to live in the best water environment ever.

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