Black Algae In Fish Tank | How to Remove? (Easy Methods)

Black algae or Black beard algae is a member of the red algae family in the Rhodophyta division. It appears black in colour just as its name suggests but sometimes it can also appear bluish or greenish. Black algae in fish tank are very difficult to remove because of their returning nature. Also, it will look quite ugly if black algae have covered your fish tank fully.

Black Algae in Fish Tank

If you have black algae in your fish tank and you tried removing it but it keeps coming back then this blog post will be helpful for you. We have listed all the permanent methods that you can use to get rid of black algae in your fish tank.

Also read: Can Fish Drown? | An Intriguing Quest! (How to Prevent?)

Black Algae in Fish Tank (How to Remove?)

Black algae not only spread to fish tanks but can also be found in swimming pools and ponds. They mostly grow in tropical and temperate conditions and first can be observed as tiny spots on the edges of leaves and then slowly they start to turn into a big fluffy bush. Black algae are very soft or slimy to touch but don’t confuse it with staghorn algae as they grow in a wired structure and are not hairy.

black algae

Causes of Black Algae

These are some of the major causes of black algae:

Low CO2 Level in the Water

This is one of the major reasons for the growth of black algae in fish tanks. Low or unstable CO2 levels along with poor water circulation make it difficult for plants to perform photosynthesis. Low CO2 levels can be because of a frequent water change which can cause imbalance or it may be because your Injected CO2 tank is running low or if you don’t use one try other methods of increasing CO2 in water.

Lighting Conditions

Black algae mostly grow in places with light all the time. If your fish tank has live plants and your lights are turned on most of the time then this might be the reason for black algae growth in your tank. Most plants just need 8 hours of light, more than that will give Black algae a place to grow.

How to Get Rid of Black Algae/ Black Beard Algae? (Permanent Methods)

Black algae should be removed properly if you don’t want them coming back. We have mentioned below all the methods which can permanently fix your black algae problem.

Using Hydrogen Peroxide (h2o2)

You can get hydrogen peroxide at any drug store near you. It is the easiest and most successful method to get rid of Black algae. Add 10ml of undiluted 3% hydrogen peroxide in 15 gallons of water directly to the tank and mix it. Hydrogen peroxide does not harm live plants but it might fade a bit. If there is a sensitive plant you can use it in a 1:3 ratio of hydrogen peroxide to water.

hydrogen peroxide

Hydrogen peroxide also does not cause harm to your fishes but as for precaution, I will advise you to take them out while doing this process. Black algae are very hard to get rid of so you will need to repeat this every day for 3-4 minutes till the algae disappear. 

Reduce Phosphate (po4) Level in the Water

The major reason which can cause an increase in phosphate level in your fish tank is leftover food and tap water. Phosphate is a by-product of decaying plants, leftover food and fish waste. You should clean your tank thoroughly using a brush to clean unreachable places and small particles of waste. 

If cleaning your tank isn’t working then the problem might be because of your tap water. In some places, the local authority mixes phosphate in water to prevent corrosion in pipelines. The ideal phosphate level should be below 1ppm, above this will give black algae a suitable environment to grow. If the problem is with your tap water then you can change the source of water and if this is not possible try a phosphate absorbing media that will fit in your filter. 

Boosting CO2 Levels in the Fish Tank

Aquatic plants need CO2 to get nutrients and grow, whenever the CO2 levels are low they find it tough to extract nutrients and this is where t black algae come strong. You can increase the CO2 level in your fish tank using a gas tank or by simply using Seachem Flourish Excel. Just make sure you use the correct dosage of Seachem Flourish Excel ( 20-25ppm ). 

seachem flourish excel

Increased CO2 levels will give a boost to your aquatic plants and the black algae will start starving which can also be beneficial if you have black algae eater fish in your tank.

Black Algae Eating Fish

Some fish breeds feed on black algae, the most famous one is Siamese Algae Eaters. But just as humans fishes do have preferences too in terms of food, if CO2 levels in your tank are low then the black algae would become hard and uneatable for siamese algae eaters. You can use Seachem Flourish Excel to boost CO2 levels. After the black algae become soft then the Siamese algae eaters will start feeding on algae slowly.

siamese algae eater fish

Some other black algae eating fishes are: 

  • Black Molly
  • Chinese Algae Eater
  • Twig catfish
  • Bristlenose pleco
  • Rubber lipped pleco
  • Pigmy suckermouth
  • Rosy Barb
  • Cherry Barb
  • Common Goldfish

Heat Treatment

This is one of the easiest methods you can try. Find a temporary living place for your fishes and live plants, as this method cannot be done to live plants if they have black algae. Place a heater in your fish tank and heat the water from 45°C to 50° C. The black algae will slowly burn and die in 30 to 40min. 

heat treatment

NOTE: Clean the tank and change the water fully after heat treatment to avoid any black algae particles left out.

These were some of the methods you can use to permanently get rid of black algae in your fish tank.

How to Prevent Black Algae?

These are some of the things you should do to prevent black algae in your fish tank:


Prevent overfeeding because leftover food can increase phosphate levels in the water.

Clean New Plants

Before introducing any new live plant in your fish tank make sure you clean the plant in hydrogen peroxide to avoid any risks.

Aquarium Lights

Always keep the aquarium lights on according to the plant needs and not all the time.

Keep Tank Clean

Always keep your tank clean because waste products can cause phosphate increase and change the water by 50% once a week.

Quarantine New Plants and Fishes

Whenever you buy a new plant or fish, before introducing them to the tank, quarantine them in the same bag for at least 24hours.

FAQs | Black Algae In Fish Tank

Is Black Algae Bad for Fish?

No, black algae are not at all bad for fish. They even swim and hide between black algae.

What Kills Black Algae in Aquarium?

Hydrogen peroxide (H2O2) kills black algae in aquariums. 


Black algae in fish tank are something you would not like to see. However, controlled growth of black algae can even be used for decoration purposes in tanks even fishes love to play in between them. You can use the methods listed in this blog post to get rid of Black algae permanently from your fish tank. If you have any questions regarding the black algae problem, comment down below.


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