How to Get Rid of Brown Algae in Fish Tank?

Are you tired of brown algae taking over your fish tank? Don’t worry, you’re not alone.

Brown algae, also known as diatoms, can be a common annoyance for aquarium enthusiasts. Not only does it look unsightly, but it can also hinder the health of your fish and aquatic plants.

In this article, we’ll help you understand what causes brown algae and how to prevent it from plaguing your tank. 

Fear not, with the right tools and knowledge, you’ll be able to solve this problem and keep your fish tank crystal clear.

What Is Brown Algae?

Brown algae, also known as diatoms, are a common type of algae that can bloom in your fish tank. 

They typically appear as a brown, slimy film on tank surfaces, ornaments, and even plants. 

While these diatoms can be unsightly, they are usually harmless to fish and can even be beneficial to the tank’s ecosystem.

There are a few factors that contribute to brown algae growth in your aquarium. 

Nitrate buildup from fish waste or uneaten food can cause brown algae blooms. Furthermore, cycling a new tank takes around four to six weeks and during this time, brown algae can occur naturally as the tank’s system matures.

To help prevent brown algae in your fish tank, ensure it receives at least eight hours of light per day. 

Additionally, as your tank matures, plants and green algae will compete for nutrients, which can eliminate brown algae naturally.

What Causes Brown Algae in a Fish Tank?

What Causes Brown Algae in a Fish Tank

There are several potential reasons why brown algae might turn up in your fish tank. 

Brown algae are often present in newly set-up tanks. But can also be caused by light and nutrient imbalances, poor tap water quality, and some types of substrates.

Silicate in the Water

Brown algae or diatoms in your fish tank are often caused by excessive amounts of silicate in the water. 

Silicate, also known as silica, is a common component present in tap water and other water sources. 

It can create an ideal environment for the growth of diatoms, leading to unsightly brown algae blooms. 

To prevent this, it’s important to test your water for silicate levels and use silicate-absorbing media or a high-quality reverse osmosis system to filter your tank water if necessary. 

Additionally, maintaining good water quality and performing regular water changes can help prevent excessive silicate buildup and brown algae growth.


Another factor contributing to diatom growth is the presence of nitrates. 

As a byproduct of fish waste and uneaten food, you may observe nitrate buildup in your aquarium. 

High nitrate levels can create favorable conditions for diatoms to thrive. 

Maintain regular water changes and monitor your nitrate levels to keep them in check.

Poor Lighting

Believe it or not, insufficient lighting can also lead to brown algae problems. 

When your aquarium lacks proper light, healthy green algae struggle to grow and compete with diatoms for nutrients. 

Ensuring that your fish tank has at least eight hours of light per day can help prevent this pesky issue.


Last but not least, elevated phosphate levels play a role in promoting brown algae growth. 

Phosphates often come from fish waste, uneaten food, and decaying plant material. 

To minimize these algae-friendly nutrients in your aquarium, stay vigilant with cleaning, feed your fish properly, and consider using phosphate-absorbing products, like this one.

In a nutshell, brown algae in aquariums are mainly caused by excessive silicate, nitrate, and phosphate levels combined with poor lighting. 

By addressing these factors, you’ll be well on your way to maintaining a clean and healthy fish tank environment for your aquatic friends.

How to Remove Brown Algae from the Fish Tank?

There are several methods to remove brown algae from your fish tank. 

In this section, we’ll talk more about manual removal, using bleach, and the introduction of algae eaters to the tank.

Manual Removal

The first step in removing brown algae is to manually clean your aquarium. 

You can use a soft sponge or an algae scraper, like this one sold on Amazon, designed for aquarium use. Make sure to thoroughly clean the glass, decorations, and any equipment affected by brown algae.

Additionally, removing any debris and uneaten food from the bottom of the tank can help to prevent the further growth of algae. 

A siphon vac can be used to clean smaller pebbles and gravel substrates. This siphon vacuum is highly recommended and can be found on Amazon.

Performing regular water changes can also help keep brown algae at bay. 

Replace approximately 25% of the tank water with fresh, dechlorinated water every one to two weeks to maintain water quality and reduce the risk of diatoms (brown algae).

Using Bleach

Using bleach may be an effective way to get rid of stubborn brown algae buildup on decorations, equipment, or filters. 

However, use caution while using bleach and follow these steps:

  1. Remove the affected items from your tank.
  2. Prepare a 10% bleach solution by mixing one part bleach with nine parts water.
  3. Soak the items in the bleach solution for 5 to 10 minutes.
  4. Thoroughly rinse the items in dechlorinated water to remove any bleach residue.
  5. Allow the items to air dry completely before returning them to the tank.

Note: Using bleach on live plants is not recommended, as it can harm or kill the plants.

Adding Algae Eaters to the Tank

Introducing algae-eating fish to your aquarium can help control brown algae growth. 

Some popular options include otocinclus and plecostomus fish. 

Before adding any algae eaters, make sure they’re compatible with your current tank inhabitants. 

Moreover, remember that algae eaters alone won’t completely solve the problem; maintaining proper tank conditions and water quality is equally crucial for preventing brown algae from reoccurring.

Tips on Preventing Brown Algae

To keep your fish tank free of brown algae, follow these simple tips:

  1. Lighting: Ensure your tank gets at least eight hours of light per day. This helps plants and green algae outcompete brown algae for nutrients, like nitrite and nitrate.
  2. Water Quality: Maintain a balance in your aquarium by mixing conditioned tap water and RO water during water changes. This reduces nitrate and silica levels that contribute to brown algae growth.
  3. Feeding: Be mindful of how much food you give your aquatic friends. Overfeeding can lead to excess nutrients, promoting brown algae growth.
  4. Cleaning: Regularly vacuum the gravel and clean ornaments to remove debris and prevent brown algae buildup.
  5. Patience: Remember that aquariums take four to six weeks to cycle. Brown algae often disappear as your tank’s system matures and its bacteria and nitrogen cycle establish.

By implementing these tips, you’ll maintain a healthy aquatic environment and lessen the chances of brown algae taking over your fish tank.

FAQs About Brown Algae in Fish Tank

Is Brown Algae Unhealthy?

Brown algae are not necessarily unhealthy for fish or aquariums. In fact, they can be a natural part of the ecosystem and can indicate a healthy balance of nutrients in the water. 

However, excessive brown algae growth can be unsightly and may indicate an imbalance in the aquarium’s water chemistry. 

It’s important to maintain good water quality and perform regular aquarium maintenance to prevent excessive algae growth. 

Does too much Light Cause Brown Algae?

Excessive light can contribute to the growth of brown algae in aquariums. Diatoms, the type of algae that causes brown algae blooms, require light for photosynthesis, and too much light can lead to overgrowth. 

It’s important to maintain a consistent lighting schedule and avoid leaving the aquarium lights on for extended periods of time. Using a timer to regulate the aquarium lights and reducing the amount of light exposure can help prevent brown algae blooms.

Additionally, it’s important to perform regular water changes and maintain good water quality to prevent excessive algae growth. 

Does Brown Algae Ever Go Away?

Yes, brown algae can eventually go away. It generally takes about four to six weeks for a new tank to establish its bacteria and nitrogen cycle, at which point you may see a reduction in brown algae.

As your fish tank matures, the development of beneficial bacteria, aquatic plants, and even green algae can help compete for the nutrients required by brown algae, eventually out-competing it and causing it to disappear.

During this time, you can remove the brown algae manually by scrubbing decorations and tank surfaces. 

If the algae stubbornly cling to the gravel, you might want to remove the substrate and clean it separately. Just remember to be patient and persistent with your maintenance, and the brown algae should eventually diminish.