How do I eliminate the black algae from my planted aquarium?

An aquarium is a source of great joy. Even the process of cleaning an aquarium can be therapeutic…until you spot an ever-growing cloud of the black algae.

Your regular cleaning products and methods don’t seem to work on it. So, how do I eliminate the black algae from my planted aquarium?

There are several ways to remove black algae from your aquarium and prevent it from forming again. For starters, you need to adjust phosphate level and light intensity to make sure it doesn’t grow any further. Then you can bring in fish that can eat the algae away. They can do a decent job at keeping the tank clean.

Here it is worth noting that the black algae can always return. So, you need to focus not just on elimination but also on prevention. And for that, you need to know what this algae is, where it comes from and how does it grow in your tank.

Let’s get to know the dark enemy.

What Is This Black Thing in My Aquarium?

Black algae is also known as black beard algae. Take a closer look at the thing and you will know from where it got its name. From far away, it looks like black mold, though it is actually dark bluish green in color. Interesting fact: It actually belongs to the red algae family.

 It is like those unwanted guests who appear when least expected, overstay their welcome, and keep coming back to pester you.

Another interesting fact about this black algae is that it grows too fast and grows on virtually any surface. So, don’t be surprised to find all your tank toys and plants covered in a patches of hair.

There can be a lot reasons behind that growth in your aquarium. It is more common in tanks with too many fish and too little plants. However, sometimes even too much light can be the culprit. No matter the reason behind its infestation in your aquarium, you need to make sure you eliminate every single one of those possibilities to make sure the algae is gone for good.

So, that means you need to follow more than one steps to completely eradicate the black algae problem. Let’s see where to begin.

Scrap as Much Algae Out as Possible

First, you need to take out all the decorations and plants from the aquarium. Do not try to scrub the algae while those things are in the tank. That will just spread the algae on items that aren’t affected yet. Once all the items are removed from the tank, you can scrap the algae out with an algae brush. Remove as much as you can.

Clean the gravel and filter as well and do a water change. The waste food stuck in gravel is what algae feeds on.

Clean All the Items with Peroxide

If you see the algae on only some leaves of a plant, it is best to cut all those leaves and parts out. That is even more effective than cleaning.

Now for cleaning the decorative items, the best solution is hydrogen per oxide. You can get any over the counter 3% per oxide for this purpose. Soak all the items in it for 3 minutes and rinse thoroughly.

Peroxide is safe because it almost completely rinses out with no residues to worry about. Plus, it does a good job in removing the black algae almost entirely.

Dim the Lights

Your aim should be to make the tank environment as uncomfortable for the algae as possible. Light is one thing the black algae love. They need light to thrive and grow. So, you need to dim the lights a bit.

If your aquarium is closer to a source of natural light, like a window, move it away. If your LED lights are too bright, switch to dimer ones. Don’t leave the lights on all the time. For instance, if you keep them o for 8 hours, cut it down to 6.

Regulate Phosphate Level

Higher phosphate level is one of the leading cause of black algae infestation in your aquarium.

Now, there can be many reasons why your tank has more phosphate in it. The very first being the tap water in your area. In some regions, phosphate is added to tap water to prevent corrosion of old lead plumbing.

But that isn’t the only reason. Phosphate comes from the decaying waste in the tank. Everything from decaying plants to food waste will contribute to increased phosphate levels.

You need to make sure the phosphate level in the tank is below 1 ppm. Anything higher than that encourages algae growth.

If your tap water has phosphate level higher than that, use a different source of water or use a saltwater carbon media with phosphate absorbers for your filter.

Also, clean your aquarium more often to make sure the waste and debris doesn’t stay long enough to create phosphate buildup.

Introduce Some Liquid Carbon

Scraping doesn’t really remove all the algae. Now, you need to make sure it doesn’t grow. In fact, you can starve it to death with some liquid carbon. It is a great way to empower other plants in the tank and weakens the algae. When algae overpower your plants in this game, it becomes stiff and even harder to remove.

With a higher CO2 level in the tank, other plants can take more nutrients from the tank, which in turn leaves less for the algae. CO2 regulators are easily available and many are even marketed as algaecides.

Another advantage of CO2 injection is that it will make the black algae too weak and soft. If you have algae eaters in the tank, they will devour this soft algae much quickly.

So, basically you get healthier plants, weaker algae, and happier fish.

Bring in the Algae Eaters

If you don’t already have algae eating fish in your aquarium, you need to bring some now. And if you already have a few, bring in the ones that specifically love the black algae.

Siamese Algae Eaters are your best bet. Black molly, twig catfish, rosy barb and pygmy suckermouth are good options. Common goldfish and shrimps are also algae eater but they are too slow to make any real difference.

Related Questions

Is the black algae harmful to fish in the aquarium?

No, the black algae is not harmful to your fish. Many fish devour it as food. Many enjoy its presence in the tank and love to hide behind its long fibers.

Is the black algae harmful to plants in the aquarium?

Yes, the black algae can harm live plants in your aquarium in several ways. As it grows thicker on the edges and walls, it blocks out the light and hinders the process of photosynthesis. Plus, it may also absorb nutrients that are meant for your plants.

Is it important to remove the black algae from my aquarium?

If you don’t have any aquatic plants in the tank, you do not have to worry about the algae causing any real harm. However, it can grow quite fast and soon your entire aquarium will be covered in ugly looking beard.


To conclude, the black algae survives because it finds the right conditions in your tank. The best way to eliminate and prevent the black algae infestation is to improve your tank conditions. Regulate carbon and phosphate level and the algae won’t find the right environment to thrive or even survive. Bring in a few algae eating fish and you have your own cleaning crew in the tank.


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