Black Hair Algae 101: Causes, Removal Tips & More

Disclosure: When you purchase something through my affiliate links, I earn a small commission. As an Amazon Associate, I earn from qualifying purchases.

Black hair algae are quite a popular nuisance in home aquariums. To be honest, when I first encountered this organism, I had no idea what it was or how to get rid of it.

Therefore, to make it easier for you, I decided to collect all the important information in one article.

I will cover what black hair alga is, what causes it, what fish eat it, and what steps you can take to get rid of it. So, without further ado, let’s dive into it.

It is pretty common to find black hair algae (also known as black beard algae) growing on aquarium plants.

What Are Black Hair Algae?

Black hair algae have many names. Some people call them black beard algae. Others use the term ‘Black Brush Algae.’ They are the same things.

This is what you should know about the organism:

1. Classification 

The algae’s scientific name is ‘Audouinella.’ It is part of the red algae family, which constitutes algae from freshwater and marine environments.

Named by J.B Bory de Saint-Vincent in honor of J.V. Audouin (Dictionnaire Classique d’Histoire Naturelle co-editor), black algae reproduce asexually.[1] 

2. Appearance

As their name suggests, black algae are black. However, they can manifest dark green and gray tones.

They look like spots when they first appear in an aquarium before morphing into raised Stubbe on leaves.

If they go unchecked, the algae will turn into tufts along the leaf’s edges, mimicking a beard.

The algae will continue to grow until the strands are long and flowing, comparable to sleek, luxuriant hair.

Black algae will cover every surface it can reach, including rocks, driftwood, and aquarium equipment.

3. Home Aquariums

Black hair algae are not toxic. They won’t harm fish or shrimp. In fact, some aquatic creatures survive by eating algae, including black hair.

That being said, the organism is unsightly, especially when it grows to a point where it covers every visible surface, including snail shells.

But that is the least of your worries. 

Black hair algae will cover the plants, preventing light from reaching them while simultaneously absorbing the nutrients they require to thrive and survive.  

Aquatic plants attract algae because they eject excess metabolites through the leaves, which algae can consume.

This should encourage you to remove black hair algae from the aquarium. Some aquarists use the organism to improve their tank’s aesthetic value. 

But they have the skill and experience to control the algae. In the hands of a new aquarist, black hair algae will overrun the tank.

Photo of black hair algae growing on aquarium rocks.

What Causes Black Hair Algae In Aquariums?

Black hair algae have various sources. Some of them are easier to combat than others. Look for the following:

1. Spores

Black beard algae appear in many tanks because algae spores hitched a ride on new plants, decorations, and fish.

Many algae species use this method to spread, which is why experienced aquarists quarantine their plants and fish before adding them to the main tank.

They will also scrub new plants and decorations thoroughly, stripping them of chemicals, bacteria, parasites, and algae spores.

But even if they enter the tank, those spores won’t grow unless you expose them to the right (or wrong) conditions.

2. Excessive Exposure To Light

Excess light encourages algae growth. Algae are more likely to run amok if you expose your tank to direct sunlight. 

Black hair algae are even more dangerous because they can grow in dim lighting. The organism uses all visible light for photosynthesis.

3. Nitrogenous Compounds & Phosphate

Your biggest concern here is not excess nutrients but rather an imbalance in the nutrients. For instance, black hair algae thrive in environments with low carbon dioxide levels.

In fact, some aquarists interpret the presence of algae as a sign of trouble because plants consume CO2, and low CO2 levels can affect their health.

But algae will also grow in aquatic environments with unstable CO2 levels. The black brush algae will multiply even as your plants perish (because they can’t perform photosynthesis). 

Naturally, they love nitrates and phosphates. But you need a combination of the two.

Tom Barr, Gregg Watson, and experts from the Plant Guru (Barr Report) performed a study to determine whether excess phosphates cause black beard algae.[2]

Even though the researchers recorded robust plant growth, algae did not appear, proving that it takes multiple factors to spark algae growth. 

Those factors take root because of poor maintenance. You are more likely to observe black beard algae in an overstocked tank with rotting organisms and poor circulation. 

Sometimes black hair algae will develop a whitish color at the tips.

How Do I Get Rid Of Black Hair Algae?

Fighting black hair algae is difficult because they use some components that plants require. You should proceed carefully. Consider the following:

1. Elevating The CO2 In Your Tank


  • Install an airstone to create more agitation in your tank.
  • Make sure the bubbles reach the surface, allowing CO2 to dissolve.
  • Increase the number of fish in your tank (a natural way to increase CO2).
  • Consider adding snails and shrimp to your fish tank.

You won’t kill black beard algae by boosting CO2 levels. However, you can slow their growth. More importantly, higher CO2 levels will boost plant growth. 

A study from Arizona State University’s School of Life Sciences showed that plants could extract carbon from bicarbonate in environments with limited carbon dioxide.[3] 

In other words, they will survive tanks with limited carbon dioxide. But they are more likely to succumb to algae infestations. 

By boosting CO2 levels, you make the plants stronger, and stronger plants can outcompete black brush algae for the nutrients in the aquatic environment.

The methods you use to boost CO2 levels will depend on the resources at your disposal. Some people use CO2 injectors. Others prefer liquid carbon. 

2. Applying Carbon-Based Products

While I haven’t tried this myself, many of my friends recommend the Seachem Flourish Excel (link to Amazon) to fight black hair algae. 

But the quantities matter. Follow the instructions carefully to avoid overdosing. Some chemical products are dangerous to fish and shrimp when you apply them in large quantities.

Use these products at night, when the lights are off. You know you’ve succeeded once the black algae turn red or purple.

3. Using Hydrogen Peroxide

People use hydrogen peroxide to clean wounds. In aquaculture, the University of Florida has identified the chemical compound as an effective weapon against parasites, bacteria, and fungi.[4]

But what about algae? 

Vass Levente and Ioan Bud from the University of Agricultural Sciences and Veterinary Medicine explored the subject and found that hydrogen peroxide attacked filamentous alga without harming fish or plants.[5]

A team of scientists from the John Innes Center (and the University of East Anglia) realized that hydrogen peroxide could overcome algae such as Prymnesium parvum after performing a study designed to protect the angling economy from algal blooms.[6]

If hydrogen peroxide can fight algae on a relatively large scale in Norfolk and Suffolk, it can protect your aquarium from black hair algae. 

At the very least, you should soak new decorations in hydrogen peroxide. Either way, here is an excellent video explaining how to use it against algae: 

4. Removing Nitrogenous Compounds


  • Perform weekly water changes of about 15 to 20 percent.
  • Siphon the substrate at least once a week using an aquarium vacuum device.
  • Manually remove debris and leftovers seen on plants and decorations.
  • After each maintenance session, measure the ammonia, nitrite, and nitrate.
  • Ammonia and nitrite should be at 0 ppm, while nitrate remains below 20 ppm.

Along with installing decent filters, you should perform regular water changes to combat nitrogenous waste.

Also, techniques like reverse osmosis can purify the water beforehand, removing dangerous toxins that encourage algae growth. 

You should also invest in filter media that absorb nitrates and phosphates. I personally use the Fluval External Power Filter Pre-Filter Media (link to Amazon).

5. Feeding Your Fish Adequately

Avoid overfeeding. Give the fish food they can finish in a few minutes. 

Overfeeding produces more leftovers. Those leftovers will rot and produce ammonia, nitrites, and nitrates. 

Remember to vacuum the substrate. Leftovers typically sink to the bottom and hide in the substrate. 

6. Reducing Lighting Exposure

You don’t have to remove the artificial lights. But because light encourages algae growth, your aquarium will benefit from three days of darkness.

This involves turning the lights off, throwing a blanket over the tank, and boosting the oxygen supply. You can perform a water change afterward.

Pro Tip: If you want to get rid of hair algae, here’s a step-by-step guide where I explain how to do it (with some great videos for a better understanding).

What Fish Will Eat Black Hair Algae?

Fortunately, this organism has plenty of predators, including: 

  • Black mollies
  • Crossocheius siamensis
  • Twig catfish
  • American flagfish
  • Cherry barbs
  • Goldfish
  • Bristlenose plecos
  • Angelfish

You can also rely on shrimp and snails. But these creatures cannot survive on algae alone. You must supplement their diet with external food sources. 

Although, they are more likely to survive for several days, possibly even weeks, without external food sources if the tank has a healthy population of black hair algae.

Useful info: If you wish to use algae eaters to control the hair algae situation in your tank, here is an article where I listed the best species for this job.

How To Remove Black Hair Algae From Aquarium Plants?

People don’t typically remove black hair algae from plants. You can try plucking the strands and patches off the leaves. Some people use brushes and sponges. 

But this process is time-consuming and not feasible if you have large tanks with a sizable collection of plants.

You are better off trimming the leaves with the hair algae. Keep trimming until all the sections with algae are gone. 

But what if the entire plant is compromised? In this case, take it out, but don’t throw it away. Dip the plant in a hydrogen peroxide solution. 

Aim for 3 percent hydrogen peroxide. The plants should be rinsed thoroughly before you re-introduce them to the aquarium. A 3-minute bath is enough to kill the algae.

If you can’t move the plants, treat the entire aquarium with hydrogen peroxide. You need 10ml for every 15 gallons of water, assuming you have 3 percent hydrogen peroxide. 

Hydrogen peroxide sounds dangerous, but it is harmless to most aquarium plant species.

Trimming plant leaves may be the fastest way to get rid of black hair algae in a planted aquarium.

If you found this article helpful, these may also interest you: