Black Algae in Fish Tank: How To Get Rid of It (Permanently)

black algae in fish tank
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Black beard algae is a nuisance that appears from nowhere and spreads within days. It clings to any hard surface and will often grow back after you scrape it.


If there are black algae in your fish tank, you must be looking for ways to fight this fuzzy monster before it gets out of hand.

This article highlights what causes black beard algae and ways to get rid of it. But first, here is a quick overview of this alga.

What Is Black Beard Algae?

Black beard algae or black brush algae (BBA) belongs to the red algae family.

This soft, slippery alga appears as black, bluish-green, blackish-green, or brown-gray spots. But, it turns red as it dies.

black algae in a fish task

This algae starts as small, dark spots that transform into fluffy tufts to look like a beard or brush. BBA resembles a hipster beard or lush, flowing hair. With time, it engulfs the aquarium decoration, equipment, plants, and viewing panes.

Black beard algae grow fast and infest freshwater and saltwater aquariums. It is not harmful to fish as most fish are happy to hide and swim in the long, wiry hairs.

However, fully-grown algae are dangerous to aquarium plants since it prevents them from getting enough sunlight. Light is essential for photosynthesis, and without it, plants die.

Beard algae are stubborn and may come back after it is removed. If you are wondering what brings about these challenging algae, here are five causes.

Causes Of Black Algae In A Fish Tank

Unstable Levels Of Carbon Dioxide

Unlike live plants, black algae thrive in environments with fluctuating levels of carbon dioxide. It takes advantage of low carbon dioxide levels to multiply.

The unstable levels of CO2 may be a result of a large water change, a blocked or an empty CO2 canister, or injecting a low CO2 dosage.

Excess Phosphate

In some cities, the old plumbing lead pipes are highly corrosive. Authorities add phosphate into the water to prevent corrosion and lead poisoning.

You can test your tap water to identify whether it is the cause of the frequent algae explosions. If the phosphate levels are above 1 ppm, then the tap water is boosting algae growth in the tank.

black algae in aquarium plants

Moreover, excess leftover fish food, plant waste, and fish waste decay to produce phosphates. This by-product provides a perfect recipe for beard algae to grow.

Introduction Of Contaminated Surfaces

Contaminated aquarium accessories or plants can introduce black beard algae to your fish tank. If a new fish or plant has traces of spores, they may grow and develop into a black algae outbreak.

Too Much Lighting

Fish tanks with light-sensitive fish are particularly prone to black beard algae as it thrives in excessively lit environments. Constant exposure to direct sunlight and LED light helps black algae to grow rapidly.

Excess Nutrients

Fish tanks with too many nutrients can lead to the growth of black brush algae. Excess nitrates may be a result of infrequent water changes or overfeeding your fish.

How To Get Rid Of Black Beard Algae In An Aquarium

Have you identified how black beard algae came to be in your fish tank? If yes, here are nine ways you can remedy the problem.

1. Scrape The Algae

If the algae has infested the tank décor, you can scrape it with an algae brush. The brush will remove the long, loose algae and reduce the spread. However, chances are that the BBA will return.

2. Remove Contaminated Surfaces

This solution is effective when black beard algae are starting to infest. It appears as small spots on plants or accessories. If you spot the algae growing on the plants’ leaves or stem, you can cut the part off and out of the aquarium.

However, if the tank is infested, this is how to treat black beard algae.

3. Use 3% Hydrogen Peroxide Bath

Regular hydrogen peroxide kills all black beard algae.


We recommend you use 3% hydrogen peroxide.

Soak the affected plants, accessories, decoration, substrates, and equipment in an undiluted hydrogen peroxide solution for three minutes.

The recommended peroxide to water ratio for live, sensitive plants is 1:3. This solution, though weak, can damage gentle plants like Japanese Moss balls.

If the fish tank has plastic plants, you can soak them in hydrogen peroxide or bleach for two minutes. The recommended bleach to water ratio is 1:20.

After the peroxide bath, rinse the treated décor thoroughly in freshwater to remove any residue before placing it back in the tank. The black algae should start fading in color within a few days and die in a month.

In addition to treating the aquarium décor, you must learn how to clean black algae from a fish tank.

4. Treat The Aquarium With Hydrogen Peroxide

Next, soak the fish tank with peroxide.

We recommend adding 10 ml of hydrogen peroxide for every 15 gallons of water.

This means that a 60-gallon tank needs 40 ml of undiluted peroxide.

When you add the peroxide into the tank, shut the pump outlet to allow even distribution of the solution. Repeat this once every three days for 10 to 21 days.

Does hydrogen peroxide affect fish or other aquatic invertebrates? No. However, you can move your pets from the treatment tank to maintain your peace of mind.

5. Boost Carbon Dioxide Levels

You can get rid of black beard algae by injecting carbon dioxide into the tank or adding liquid carbon. Although this process is not spontaneous, it prevents the growth of algae. How?

When you raise the carbon dioxide levels, the aquatic plants have an easier time competing for nutrients. This leads to the starvation and death of the algae.

However, be extra careful when pumping carbon dioxide if your tank has sensitive fish or shrimp. The additional CO2 may cause a sudden pH drop and a reduction in oxygen levels, which is dangerous for aquatic life.

6. Try Heat Treatment

If you are researching how to get rid of black beard algae without using chemicals, try using heat.

Boil the affected accessories for ten minutes to kill algae and tiny spores. However, this method has restraints because you cannot boil live and plastic plants.

Also, use a tight-fitting lid to secure the pot. Some rocks explode when subjected to high temperatures, and this is a mess you do not want to clean.

Alternatively, heat the infested tank for an hour between 110 to 120 degrees Fahrenheit. Remember to remove your fish, live plants, and plastic plants before you begin the heat treatment.

Here is a video that shows how heat treatment works.

7. Regulate Phosphate Levels

High phosphate levels from excess fish food, plant waste, or fish waste encourage the proliferation of beard algae. But you can starve the algae by preventing them from accessing these nutrients.

Take out any dead fish, invertebrate, or plant waste before they produce phosphate.

Also, avoid overfeeding your fish and maintain weekly water changes. Furthermore, constantly vacuum the areas where detritus accumulates, including the substrate.

A powerful filtration system will also help regulate phosphate levels in the fish tank. First, get a filter with phosphate-absorbing media. Secondly, ensure that the filter can pump at least four to five times the volume of the tank water per hour. This means that a 20-gallon tank will need an 80-gallon per hour filter.

Additionally, clean the filter regularly to remove any algae spores. Perform regular water changes to reduce phosphate levels.

What if your tap water has high levels of phosphate?

Substitute it with purified water by reverse osmosis or distilled water. Remember to re-mineralize the water since purification removes all minerals.

8. Reduce Light

This method is most effective in tanks without live plants. The concept of reducing or eliminating light kills black algae because it cannot photosynthesize.

aquarium with fish and plants

For starters, move the tank away from direct sunlight. Alternatively, you can block the sunlight by covering the aquarium. When black algae receive limited sunlight a day, it slows its growth rate and eventually stops.

9. Add Black Beard Algae Eaters

The Siamese Flying Fox, Siamese Algae Eater, Amano shrimp, Twig Catfish, Black Molly, Florida Flag Fish, and Nerite Snail are some of the aquatic black algae eating fish.

The Amano shrimp eat black algae faster than most fish and snails. On the other hand, Siamese Flying Fox can eat even the stiff algae, while snails only ingest dead brush algae.

Keep in mind that most algae eaters only eat soft algae. You can soften it by injecting carbon dioxide into the tank. The high CO2 levels weaken the algae to become an appealing snack. Additionally, a hydrogen peroxide bath also does the trick.

Keep in mind that adding black beard algae eaters may not be the sole solution for your fish tank. These fish may not find the algae appealing if they are well-fed. Also, they may not clear the overgrown algae as fast as you’d like.

For this reason, combine these algae eaters with a hydrogen peroxide bath or CO2 injection. Doing so will guarantee the eventual death of the algae.

Related Questions

Are black algae dangerous to fish?

No. On the contrary, many fish enjoy hiding in the long hairs while others happily look for trapped food particles in the algae.

Can you prevent black beard algae?

Sure. Always quarantine new fish for two weeks before adding them to the main tank. Clean new plants with hydrogen peroxide to get rid of algae or bacteria. Also, avoid too much light and monitor the carbon dioxide levels to prevent fluctuations.

Final Thoughts

Although black beard algae are stubborn, it is not impossible to get rid of.

You can begin by lowering the phosphate levels, which act as a catalyst for algae explosions. Or you can remove all the contaminated objects to prevent overgrowth.

However, if you seek fast results, use 3% hydrogen peroxide, heat treatment, or introduce black beard algae eaters.

Black brush algae should not transform your cute aquarium into a crazy mess. We hope this guide has enlightened you on how to get rid of black algae in an aquarium.

We welcome you to share your experience in the comment section below.

Last Updated: July 28, 2022

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