My Aquarium Water is Brown – What’s Going On?

Last Updated on 2023-08-08

Most aquarium keepers would rather not have brown water, which can give the impression of being muddy, dirty, or poorly maintained. The brown water would immediately lower the beauty of your aquarium. It can also mean that the brownish water in your aquarium water means it’s no longer safe for your fish to swim in. There are a lot of reasons why this is happening, but don’t worry! There are a lot of ways to stop it. If the water in your aquarium ever turns brown, read this article to learn everything you need to know about brown water in aquariums.

Why Is Your Aquarium Water Turning Brown?

As aquarists, we don’t really want to see brown water in our aquariums because it gives the impression that the water is stagnant and dirty, which it could be. The brown water could also hurt your fish’s health and kill them. Check out this list to learn seven of the reasons why the water in our aquarium turns brown.

1. Algae

When it comes to fish tanks, algae can be a frequent issue, especially for new aquariums. It can turn the water in your aquarium a murky brown color, harm your fish, and create a mess. Algal blooms happen when there are too many nitrates and ammonia in the water, which algae need to grow.

2. Tannins From Driftwood

Most aquariums have driftwood, which can change the color of the water. Tannins from driftwood can get into the water and turn it light brown, which is how you might describe the color of tea. But driftwood doesn’t have a limitless supply of tannins, and it would run out of tannins after a few weeks or months.

3. Dead Plants

A lot of nutrients and organic compounds are released into the water as plants decompose. This will promote the growth of bacteria, which could be harmful to your fish, and turn the water in your aquarium a brownish tinge. Check under the leaves of your aquatic plants and in the corners of your aquarium if there are a lot of plants to make sure there is no decaying plant matter hiding there.

4. Dead Animals

Like dead plants, dead animals like fish or snails that have been left on the bottom of the aquarium can also add nutrients to the water as they break down. These nutrients can cause algae blooms, which can turn the water in your aquarium brown. If you think your pet fish is dead, you should always check the places where they usually hide.

5. Tannins From Soil

If the water in your aquarium has turned brown, but your fish are fine, and there is no driftwood in the tank, the tannins in the water probably came from the substrate. Tannins could be in the substrate that was put in the tank without being washed, which would make the water in your aquarium cloudy and brown. Always wash everything you put into your tank to get rid of harmful chemicals and parasite eggs.

6. Dirty Water From Water Change

There’s also a chance that the water you put in your tank when you change the water is dirtier than the water you took out, which would make the water in your aquarium brown. Even if the water is clear, it could have had ammonia and nitrates in it and caused algae to grow when it got into the aquarium. To avoid this problem, make sure that the water you use for water changes is clean and treated.

7. Too Much Leftover Food

Algal blooms, which turn the water in an aquarium brown, can happen when there are too many nutrients in the water for the algae to grow. Even if there are no dead plants or fish in your tank, extra food that is just floating around can be broken down to give algae the nutrients it needs. Make sure to feed your fish the right amount of food at the right time. This will stop algal blooms and keep your fish’s digestive system healthy.

Gold fish or goldfish floating swimming underwater in fresh aquarium tank with green plant. marine life.

How Do You Fix Aquarium Water Which Is Turning Brown?

There’s no denying that stagnant brown water in your aquarium is unattractive. In addition, it could be hazardous to the health of your fish and the ecosystem they inhabit. If the water in your aquarium has turned brown, try one of these seven solutions.

1. Water Change

To eliminate the brown color in the aquarium’s water, a simple water change is a good way to start. This will help to reduce the concentration of ammonia and nitrates in the tank water as well as remove any floating fish waste. Don’t overdo it, though, or you might throw off the delicate ecosystem of your aquarium.

2. Boil Driftwood

There are many reasons and benefits of boiling driftwood. The tannins in driftwood can be extracted more quickly by boiling it in a large stockpot, much like a tea bag in hot water. Boiling the driftwood also sterilizes it, killing any algal or fungal spores that could potentially take hold in the aquarium.

3. Vacuum The Substrate

It’s important to vacuum the substrate of an aquarium on a regular basis. Dead plant leaves, uneaten fish food, and other organic debris all sink to the bottom of the tank, where they can decompose into harmful ammonia and nitrates. Whenever this occurs, the water will turn a muddy brown color.

4. Trim Dead Leaves of Plants

If you find dead leaves on plants, they might be what’s making the water turn brown. When this happens, you should trim it out so that it doesn’t cause ammonia and nitrate levels in the water to rise. In fact, trimming has many benefits for plants and, depending on the plant, should be done often.

5. Transfer Other Fish

Brown water can also be caused by having too many fish for the size of your fish tank. When this occurs, it’s best to move the affected fish to a new tank so that the nitrates and ammonia levels don’t rise to dangerous levels. Fish don’t get used to new places easily, which is why you need to be careful when moving them from one fish tank to another.

6. Install an Aquarium Filter

Filtration is one of the most important parts of an aquarium. It moves and cleans the water in the tank, making it safe for fish to live in. In fact, it should be in an aquarium to keep the water’s conditions stable. Installing a water filter in your aquarium can help cut down on fish waste, which can cause ammonia to build up and turn the water brown.

7. Put Activated Carbon In Your Aquarium

Activated carbon is a very porous and absorbent material that can get rid of chlorine, bad smells, and browning of water in your aquarium water. It can improve the quality and clarity of the water, which can help you keep an aquarium in good health. If you want to keep your tank water in peak condition, using activated carbon to filter it can do wonders for its clarity and purity.

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Why Did Your Aquarium Water Turn Brown After A Water Change?

Aquarium water can turn brown after a water change for many reasons. Some of these include the presence of organic matter, high levels of tannins, excess nutrients, and even old equipment. Here are some common causes for why your aquarium water may be turning brown and what you can do to fix it. 

1. Too Much Water Changed

If you change out too much of the water in the fish tank, you risk killing the fish by washing away the good bacteria and throwing off the nitrogen cycle. Brown water is often caused by the dissolution of organic matter from dead fish and other animals. Partial water changes are ideal if you maintain a clean tank on a regular basis.

2. Excess Nutrients

Excessive nutrients in the aquarium can cause your water to turn brown after a water change. These come from overfeeding and uneaten food that then decomposes, releasing ammonia, nitrates, and phosphates into the aquarium ecosystem. Regular water changes can help reduce nutrient levels in the tank.

3. Tannins from Decaying Wood

Another reason why your aquarium water may be turning brown is due to the release of tannins from decaying wood and other organic materials. These tannins can tint the water yellow, orange, or even dark brown. To reduce tannin levels in the tank, you must remove all the organic materials from the aquarium.

4. Copper or Iron Levels

Too much copper and iron in the water can cause it to turn brown after a water change. This is due to oxidation, which happens when these metals come into contact with oxygen. Using a deionizer or reverse osmosis filtration system can help reduce these levels and keep them in check. 

5. Old Equipment

If you use old equipment that is not regularly cleaned or replaced, it can lead to bacteria buildup, which can cause your water to turn brown after a water change. Make sure to clean all of the components of your tank with an aquarium-safe cleaning solution on a regular basis. 

6. Low pH Levels 

Low levels of pH in the water can cause it to turn brown after a water change. This is due to acidity, which increases when the pH level decreases. Make sure to test your tank’s pH on a regular basis and adjust it according to your fish’s needs. 

7. Algae Growth 

Algae can also cause your water to turn brown after a water change. This is because they produce tannins, which give the water its yellow, orange, or dark brown tint. Make sure to clean your tank regularly and use air stones to keep oxygen levels high so algae won’t thrive. 


Why Did Your Aquarium Heater Breaking Turn the Water Brown?

If your aquarium heater is broken, it could be that it heated the water too much. Ammonia and nitrates can get higher when there are more fish, which could be why the water is brown.

Why Did Driftwood Turn Your Aquarium Water Brown?

Like most plant matter, tannins can be found in driftwood. Ever since driftwood was a thing in aquariums, people have known that tannins can stain water brown or yellow.

Does Peat Moss Turn Aquarium Water Brown?

Peat moss, contains tannic and gallic acids that react with the bicarbonates in aquarium water to decrease the pH and the water’s hardness. The ability of tannins to stain aquarium water is well-known.


The browning of the water in your aquarium is unattractive. When you see the water in your aquarium turning brown, your initial reaction might be to panic. While water discoloration may not always be harmful, it likely will be fatal to your fish if it happens to them. The good news is that brown water in an aquarium can be easily fixed by taking care of a few simple maintenance tasks like installing an aquarium filter, performing regular water changes, cleaning your driftwood, and vacuuming the substrate. If you keep up with routine maintenance and water quality tests, you can catch water browning in its earliest stages, when it is easiest to prevent and fix.

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