Cyanobacteria is often called slime algae, but it’s actually a slime mould.

If you have cyanobacteria in your tank, it is going to look like a thin dark red slimy mould covering the rock surfaces of your tank. This indicates that your tank has a very high level of dissolved organic matter, which is a bad thing.

Typically, cyanobacteria can even outcompete hair algae. When this takes place it normally indicates an even higher level of dissolved nutrients than hair algae require. In other words, your tank is very polluted.

I’m not talking about small localised areas in your tank where you have a tiny bit of slime algae. Often in your system, you may have a location where there’s very little water movement flowing and you might get a touch of slime algae there, this is usually not a problem. That’s a microenvironment that has the perfect conditions for cyanobacteria.

It is when slime algae are covering a large portion of your tank, that you have a tremendous amount of dissolved nutrients in your system that you need to take various steps to get rid of the problem.

Your first step is to begin by syphoning off as much of the slime mould as possible, discarding the syphoned water. As you remove the slime mould, you are reducing the nutrients in your tank. You can also get some sand sifters to help move the sand around, bringing oxygen to it and helping live organisms process the detritus and other waste before the cyanobacteria do. Add carbon to the system as well to help reduce nutrients.

Slime algae > Hair Algae

Once you start to reduce the pollution level within your tank, you will begin to start to see the slime algae go away. But oftentimes you’ll see hair algae starting to grow. That’s because the level of nutrients in your system won’t support slime algae, but will support hair algae. So, it’s a normal progression as your tank goes from a high nutrient one to a low nutrient one.

But you’re going in the right direction, so don’t get discouraged. Keep reducing your nutrients through water changes, skimming, phosphate remover, etc., and soon not only the slime algae will be gone but also the hair algae.

Just make sure that the makeup water is high quality and not adding to the problem!

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