How to Deal With Black Algae in Fish Tanks

Is your fish tank infested with black algae? This type of algae species might not be as bad as you think as long as you keep it under control. Black algae in fish tanks can be tough to regulate but in this guide, we are going to take a look at some of the best ways to control and keep a healthy portion of this growth in your tank.  We are also taking a look at some methods to help you completely eliminate black algae in your tank if that is the route you prefer. 

What is Black Algae?

The scientific name for black algae is Audouinella and it is part of the genus of red algae that lives in marine and freshwater environments. This alga is often called black beard algae or black brush algae because of its unique appearance. The soft algae have a furry appearance and are slippery in nature with a black or blackish green color. It usually grows in dense patches on the surfaces and plants in your aquarium. 

These algae can be challenging to clear from your fish tank because it creates a stubborn hold on surfaces and plants. They typically start growing on the edges of plants and can quickly engulf the entire plant. 

Is Black Algae in Fish Tanks Bad?

Brush algae aren’t harmful in your tank. This type of algae won’t harm your fish, aquatic plants, or invertebrates and often acts as a food source to some types of aquatic animals. Small fish also find the growth useful since they can hide among the flowing algae furs and shrimps love to pick food morsels out from these wavy growths.

Some tank owners use this type of organism in their aquascaping. Keeping black algae on a piece of twisted wood can offer a very interesting look in your tank while a densely grown forest of algae in one corner of your tank can offer a spooky and charming overall look. 

As algae rapidly grows in your tank, it can quickly cover all tank surfaces in a blanket of fur that can make your tank look unattractive and messy. 

The rapid algae growth can change the nutrient levels in the water. When this happens, the toxin chemical levels in water might rise too which can be dangerous to your animal life. 

While a few black algae can be a good thing, too much of this growth can be unattractive and harmful. 

What Causes Black Algae on Aquarium Plants?

Black algae usually enter your tank when contaminated plants or aquatic accessories are introduced to your ecosystem. The algae will quickly spread and grow in aquariums with low carbon dioxide levels and too much light. The algae spread a lot faster in unattended aquariums and can quickly cover every surface it takes to. 

Some aquarium owners do however maintain black algae in their tanks. They allow the growths to cling to a certain surface like a piece of wood and re-introduce this growth along with the piece of wood after cleaning the tank to create a visually pleasing effect. 

How Do You Get Rid Of Black Algae in Fish Tanks

Keeping or eliminating black algae in tanks is a matter of personal taste. If you keep this growth, you might need to change the water frequently to keep the growth under control. But for tank owners who don’t want to spend a lot of time on their tanks, it could be better to clear the growth from your ecosystem.

There are quite a few different strategies that you can use to clear or contain this type of growth inside your fish tank. Let’s take a look at some of the best and easiest concepts to try.

Introduce Black Algae-Eating Fish Species

There are quite a few species of fish that consume black algae. But that being said, most of these fish species prefer the algae while it is still young and soft. They might not tackle older or longer growths of algae. This can however be a good thing for aquarium owners who want to keep a few black algae in their tank as part of the aquascape.

With some of these fish species, you also need to be very careful about the tank mates that you keep along with them in the tank. Some algae eaters like the Chinese Algae Eater are highly effective for controlling black beard algae but they do tend to lash out and kill other fish species in the tank. Others like twig catfish won’t consume quite as many algae but they are much safer thanks to their calm nature. 

Here is a quick look at some of the best black algae-eating fish species to get for your tank.

• American Flagfish
• Siamese algae eaters / Chinese algae eaters 
• Black Mollies
• Twig Catfish
• Bristlenose Plecos
• Rubber Lipped Plecos 
• Pigmy suckermouths
• Rosy Barbs
• Cherry Barbs
• The Common Goldfish

Control Your CO2 Levels

Low and unstable CO2 levels along with inadequate water circulation will encourage this type of algae growth. This can be a disaster for aquatic plants in your tank because low levels of CO2 that fluctuate keep living plants from utilizing the nitrates and light in your tank for photosynthesis and they start to suffer. At the same time, the black algae starts to explode in growth since this plant flourishes in these conditions.

To keep your carbon levels stable, you need to add quality liquid carbon to the water. This will raise the carbon levels and kill the black bristle algae. Increasing the carbon levels will also weaken the black algae so algae eaters will find these foods more appealing and the higher CO2 levels will nourish your aquatic plants to encourage healthy growth. 

Reduce PO4 Levels in the Water

Introducing liquid carbon in the water can raise your phosphate levels. High phosphate levels can be damaging to your plant and fish life. 

You can get a phosphate testing kit and test the water levels. Black algae flourish in CO4 levels of 1ppm and more so you will need to decrease these levels if you get a high test score. Here is a quick look at some good ways to reduce the PO4 levels in your tank.

• Use phosphate absorbing media in your filter and make sure that the filter turns the water in the tank at least 5 times per hour to clear out the CO4.
• Get an alternative aquarium water source. Tap water often contains high levels of CO4 which can cause a spike in levels.
• Add fast-growing aquatic plants so they can consume more nutrients in the water and starve the algae.
• Try a different fish food. Some flake fish foods contain less phosphate and are better for keeping a clean tank.
• Don’t overfeed your fish so you won’t end up introducing additional phosphate into the tank.
• Clean the filter and replace the water often to clear algae spores from the tank and to keep the phosphate levels low.

Treat Your Affected Aquatic Accessories

Over-the-counter 3% peroxide can help kill hair algae on tank accessories like ornaments or plants. You can dip aquatic accessories in this solution to kill the growth. For sensitive plants like Japanese Moss Balls or Anubias, you should dilute the peroxide to a 1:3 ratio before dipping the plants since strong peroxide can burn and kill your plants. With peroxide, there is no need for rinsing since this product leaves virtually no residue on your tank accessories. 

If you only have plastic plants in the tank then you can use bleach to treat the growth. Create a mixture of bleach and water with a 1:20 ratio and soak all tank decor for 2 – 3 minutes. Rinse thoroughly before adding these accessories to your freshwater tank. 

Use Heat Treatment To Kill Black Algae

Algae flourishes in warm water but boiling water will burn and kill these growths. If you want to kill algae on your tank accessories or clear it from your tank glass then you can give boiling water a try.

Soak tank accessories in water with a temperature of 110 degrees F and wait a while for the algae to be killed. You can also use boiling water to wash or rinse the tank walls to kill these stubborn growths but be careful not to shatter your tank. 

Be careful not to boil or burn any of your aquatic plants. These can be dipped in peroxide to kill the growths. 

Reduce Light Conditions

Eliminating light in your aquarium can kill your aquatic plants. But if you don’t have any plants or only use plastic features for tank decor then you can try to reduce the amount of light your tank gets. With less sunlight or less natural light, the black algae can’t photosynthesize and will eventually die out. 

You can turn off the light or cover the tank with a thick blanket for 3 days. After this time, you can gradually increase the hours of light in the tank. The black algae will gradually start to die out and disappear. 

Final Thoughts

Black algae in fish tanks can be stubborn but there are lots of different ways to kill or control this growth in your tank. This type of growth can be a wonderful tank feature if you have the right setup. But you don’t want to combine black algae with other types of algae like green algae because a combination of these algae species can make your tank look horrid. For better control over other types of algae, you can have a look at some of the other guides we have for you on AlgalWeb. With our site, you can find a sound solution for every common algae type that might show up in your tank.