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Why is my Fish Tank Turning Brown



Why is my Fish Tank Turning Brown

“Why is my fish tank turning brown?” This question popped into my head the first time I saw my aquarium turn brownish. Back then, I was new to fishkeeping and did not know anything at all. Over the years, I learned that the reason behind this issue is the brown algae.

Silica algae or brown algae is the reason why your fish tank turns brown. You will see this type of algae as brown patches found on the tank’s glass or in the gravel. Brown algae can also spread quickly and take over the aquarium with a dark brown coating.

The Presence of Brown Algae

The presence of brown algae can make your aquarium turn brownish in color. This problem usually exists in new aquariums as brown patches that can occur in the substrate, decorations, aquarium glass, and even in fish tank plants if the aquarium has one.

Brown algae are usually caused by a number of reasons such as high nitrite and phosphate levels in the water. It can also be caused by poor aquarium lighting since it can discourage photosynthesis in green algae which in turn helps in thriving brown algae.

Brown algae will not bring any harm to your fish. However, if left unattended, it can bring a lot of negative effects to the aquarium. It can prevent aquarium plants from performing photosynthesis which can make them die. Brown algae can also make your aquarium look dirty.

Adding Driftwood into your Aquarium

There are cases that driftwood will turn your aquarium water into a color brown. When this happens, the driftwood only releases tannins or tannic acid which usually make the water turn brownish.

But, do not worry since tannic acid will not have a negative impact on the health of your fish. It is actually healthy for your fish since tannic acid is known to have antifungal and antimicrobial properties which helps in protecting the fish.

If you do not like the color of your aquarium water, it is understandable. However, the tannic acid released by driftwood will not stay forever. As you do more water change, the brown color will be reduced overtime until your aquarium water will be crystal clear again.

Silica Buildup in Aquarium Water

When you are using freshwater or saltwater, there is a mineral called silica that comes with it. This mineral can be in the form of peebles, sand, or rocks. Silica is not harmful to fish but too much buildup in your aquarium can affect water quality and encourage the growth of brown algae.

Once the brown algae blooms, it can make the aquarium turn brown. Also, silica can build up more when you are using tap water which is rich in silicic acid. To prevent the buildup, you must do constant water changes and use chemicals that can remove it.

Why Does my Fish Tank Keep Turning Green

why does my fish tank keep turning green

Apart from turning brownish, I have also experienced my fish tank keep turning green. The reason behind it is the presence of tiny algae floating in the aquarium’s water called phytoplankton.

When they become too concentrated, these microscopic organisms can turn the aquarium water green. This situation is called an algae bloom which does not affect your fish but can turn your aquarium very ugly.

Causes of Algae Bloom that Turns the Fish Tank Green

When your aquarium has too much light, it can cause an algae bloom. Always remember that algae are a type of plant which thrives and grows under light. Having too much light can definitely help it grow.

Also, If the nutrients in the aquarium are not balanced, it can also help in algae blooms. When you put nutrients in the aquarium, the algae also feeds on it. If you are putting too many or too few, it can also affect its balance, making the algae grow quickly.

Lastly, failure to regularly clean and maintain your fish tank can also lead to the proliferation of green algae in the fish tank. Regular water change, filter cleaning, and water testing are essential. Failure to do so can help in the overgrowth of algae.

Why is my Fish Tank Foggy

There will also be some instances when your aquarium will become foggy or cloudy. This situation is normal for a new fish tank but can also happen in a well-established and old aquarium. Here are some common causes when a fish tank gets foggy:

Free-Floating Bacteria in New Fish Tank

For a new fish tank, the cause of the fogginess is the free-floating bacteria and other microorganisms trying to take advantage of the nutrients in the water. When these bacteria multiply, it can cause the water to become foggy or cloudy.
Unwashed Gravel Put in the Aquarium

Unwashed gravel can turn the aquarium cloudy when you put water in a new aquarium. The water will become foggy because of the dirt that will be transferred into the aquarium water. What you do to negate this issue is drain the tank with water and thoroughly wash or rinse the gravel until the water runs clear.


Why is the fish tank turning brown? The presence of brown algae can make some of the parts of the aquarium turn brown. There are common causes for the proliferation of brown algae, but these organisms can be prevented and removed from the aquarium.

Your aquarium’s water can also turn green when there is an algae bloom. We have presented ways and means to remove it. The water can also turn foggy for new aquariums, but this situation is just normal for a newly set up fish tank.

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