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How To Deal With Purple Algae In A Fish Tank!

As fish keeping becomes an increasingly popular hobby to people, we see more and more questions being asked from the community about the various issues that can occur in a tank regarding water parameters and algae.

With there being so many people new to keeping fish right now and algae being a constant problem, it’s easy to see why so many people have been reaching out and asking about having purple algae in their fish tank over the last few months.

Unlike some of the other types of algae that we see people reaching out about, there are a number of different types of purple algae that can occur.

This tends to make it more difficult to offer specific fixes to the problem but the general principles of keeping algae to a minimum in your tank still apply.

Still, with so many people reaching out and asking for help with purple algae in their tank, we decided that we wanted to publish our own article going over the two most common types of algae.

Our hope is that we will be able to help our readers keep them under control and drastically reduce the potential problems with a specific type of purple algae that beginners commonly have problems with.

Can Algae Be Purple?

Algae can be purple and the two most common types of purple algae in aquariums is black brush algae and cyanobacteria.

Black brush algae tends to be relatively easy to deal with for the most part but cyanobacteria can be a pain if it is left to develop and it is actually a type of bacteria rather than an algae.

The two are relatively easy to differentiate between each other as black brush algae will usually look like algae and have its plant like structure where as cyanobacteria is usually flat and sticks to the rock that it is growing on.

Black brush algae tends to grow at a steady pace too where as cyanobacteria will usually grow slowly at first until it reaches a certain mass and then its growth rate increases rapidly.

As with all types of algae, the most important thing is to try and catch it as early as possible to allow you to deal with the purple algae in your aquarium before it manages to get a foothold.

That said, some people in very specific situations may intentionally add both black brush algae and cyanobacteria to their aquariums for their visual aspects but if you are unable to identify either of these algaes then chances are, the purple algae growing in your tank is un-intentional.

Is Cyanobacteria Algae Or Bacteria?

As the name suggests,l cyanobacteria is actually a bacteria rather than an algae but it is very common for new fish keepers to refer to it as an algae.

It can grow in a number of colors depending on the tank parameters and what its growing on with green, blue, red, and brown usually being the most common with black, pink, and purple being less common.

Due to cyanobacteria being bacteria, algae eaters tend not to touch it at all so it instantly removes one of the most commonly used counters to algae for beginners.

High enough levels of cyanobacteria can be toxic enough to cause serious problems for the fish in your tank though so most people will try to deal with it as quickly as possible.

Many people think that due to cyanobacteria being a purple bacteria rather than a purple algae that it will not use much oxygen in the tank water but this is incorrect.

In some very bad situations, cyanobacteria is able to take enough oxygen from the tanks water to cause it to fall below minimum oxygen levels for some fish and cause problems.

Is Purple Algae Good?

Most algaes are considered bad but in small amounts they may not cause much of an issue.

Some people will intentionally add purple algaes to their tank to create a certain look for their aquascape but this tends to be experienced fish keepers who are able to manage the algae growth with minimal effort required and are able to control its growth with ease.

Most beginners should go with the general rule of all algaes being bad and take steps to keep the algae build up in their tanks to a minimum and this does include purple algae too.

In some cases, purple cyanobacteria in large enough amounts is able to cause skin irritation to your fish and cause their scales to start to peel off too.

Black brush algae does tend to be less of an issue though as some algae eaters will reduce its growth rate but they will usually not be enough of it to keep its growth totally under control.

Thankfully though, a dip in a 3% hydrogen peroxide solution will usually be enough to damage the cells of the purple algae enough to prevent it from growing in your tank.

If you do plan to use a dip to deal with your purple algae, be sure to do your research on how to correctly implement a dip and how to quarantine the dipped surfaces before you place them back in your normal tank.

How To Deal With Purple Algae In A Fish Tank!

The easiest ways to deal with purple algae in most tanks is good old elbow grease and to scrub it off the surfaces, especially if you keep a reef tank with rare corals or other live plants that may have problems with chemicals.

You are usually able to dip any rocks or tank decorations that have purple algae growing on them in a 3% hydrogen peroxide solution to remove the purple algae quickly too.

Purple cyanobacteria can be notoriously difficult to deal with in some tanks, especially if it has been able to grow to a level where there is a large amount of it.

Some people simply remove the surface with the cyanobacteria growing on it from their tank and throw it away as it tends to take a huge amount of scrubbing to get it off most surfaces.

Water changes can sometimes work to reduce the growth rate of cyanobacteria as it removes a large amount of the nutrients from the tank that the purple cyanobacteria requires to grow.

Depending on the stage of the cyanobacteria, water changes may be enough to deal with it completely but this is rare and plenty of scrubbing will usually be required.


That brings our article going over how to deal with purple algae in a fish tank to an end. We hope that we have been able to help you identify what type of purple algae you have growing in your tank as well as the best way to remove it. Both of the more common types of purple algae can cause some serious issues if they are left unattended so we do usually recommend that our readers work on removing them as soon as they notice them growing in their tanks.