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How To Treat Black Spots On Aquarium Plants!

Not only are more and more people starting to get into the fish keeping hobby but more and more people are also starting to add live plants to their tanks rather than fake plants.

This is great to see as live plants are able to add oxygen to the water for your fish while also providing some excellent cover for the smaller fish to relax and hide.

One of the drawbacks of having live plants in your aquarium is that it can be easy for them to suffer from various types of algae, especially while you are a beginner fish keeper.

We have noticed a spike in the number of people reaching out and asking for advice on treating black spots on aquarium plants recently so we wanted to make that the main focus for today’s article.

Thankfully, it is relatively easy to remove the black algae that cause the black spots on your aquarium plants with minimal risk to your plants or fish so we have decided to publish this dedicated article on going over the exact process to help as many of our readers as possible.

Getting rid of black algae is very beginner-friendly too so the vast majority of our readers should be able to quickly and easily treat the problem without issue.

What Causes Black Spots on Aquarium Plants?

The most common cause of black spots on your aquarium plants is black beard algae but there are a number of other less common black or dark brown algaes that can also cause this effect.

Black beard algae is very common and usually added to your aquarium when adding new live plants, substrate or rocks that have not been dipped correctly prior to being placed in your tank.

Although black beard algae is very common, it is thankfully very easy to treat with the other black and dark brown algaes that can cause spots on your plants also being easy to treat with the same treatment usually being recommended for all options.

Just because you do end up with an algae bloom in your tank does not necessarily mean that you have done anything wrong either. We commonly see people new to fish keeping thinking that it is their fault that they have a problem with algae but it does take time to build up the experience required to correctly manage it.

Even experienced fish keepers can end up having problems with some types of algae and black beard algae sports can be surprisingly resilient.

Although it is not confirmed, we have actually seen people report that they think their outbreak of black beard algae was down to a new fish eating a spore, passing it, and then the spore activating resulting in a breakout.

How Do I Get Rid of Black Spots on My Aquarium Plants?

The easiest way to deal with black beard algae or any other algae breakout on your aquarium plants is to dip them in a 3% hydrogen peroxide solution for around three minutes.

This is generally enough to destroy the cells of all types of algae that commonly live on plants while also not doing any harm to your plants either.

There are a number of suitable 3% hydrogen peroxide solutions on the market that you are able to use with your aquariums live plants.

Always remove the live plants and decorations that are having problems with the algae breakout from your main aquarium for the dip and put them into a spare container.

Add the hydrogen peroxide solution to the container and let it site for three minutes before emptying the hydrogen peroxide and filling it with fresh water.

Let the freshwater site for around an hour and then empty it and refill the container will fresh water and let it site overnight.

At this stage, some people do add the live plants back to their aquarium but we usually recommend that you empty the fresh water one last time and then refill the container and let it site for another day to ensure that all hydrogen peroxide has been removed.

If this sounds like too much effort then you are able to try a direct to tank product like algaefix but it tends not to be anywhere near as effective as an actual hydrogen peroxide dip.

Is Black Algae Harmful To Live Plants?

Black algae is generally not harmful to live plants provided that it is treat quickly in a suitable manner.

If the black algae is left to develop on the live plants in your aquarium then it can start to cause problems due to taking nutrients and light away from the actual live plant but even then, many live plants can recover once the algae has been removed.

We know that the hydrogen peroxide dip can be intimidating for people who are brand new to fish keeping but it really is a very beginner friendly process that is very easy.

Just remember the rule of three, a 3% hydrogen peroxide solution for 3 minutes with 3 days of fresh water baths before re-adding the plant back to your tank.

If you are worried about the hydrogen peroxide still being on your plant then you are able to use a water test kit on the container that you have used for your dip to see if there are any major issues with the water.

This can add the boost of confidence that some people need on their very first dip to know that the hydrogen peroxide has been washed off and the plants are safe to put back in your tank.

Is Black Algae Harmful to Fish?

Most types of black algae are not harmful to fish with some algae eaters actually eating black algaes such as black beard algae.

In very bad cases the algae may remove enough oxygen from the water of your tank that it ends up causing problems with the oxygen available for your fish but this is very rare and usually takes a long time for the algae to build up to such a level.

Still, it is usually recommended that you do try to treat the algae breakout as soon as possible to prevent it from getting worse.

It can be done as a part of your regular tank maintenance when you clean your tank and you remove the plants for a hydrogen peroxide dip to get the situation under control.

We would usually recommend that you actually remove all live plants and decorations if possible even if you don’t see black beard algae growing on them. Just because the algae has not taken hold yet does not mean that the spores are not on your other live plants and that they will break out within a few days.


That brings our article going over how to treat black spots on aquarium plants to an end. Thankfully, unlike some other types of algae breakouts, it really is very simple and strength forward to fix as black beard algae is generally easy to deal with via a standard hydrogen peroxide dip. Black algae does usually only mount to your live plants and decorations too leaving your fish alone making it easier to deal with for the most part too.