Cyanobacteria Outbreak Help!


New Member
May 15, 2018
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Texas, USA
I have in my tall 20 gallon tank what I believe to be as cyanobacteria. It's a green, slime-like film covering the gravel on the bottom of my tank. It appeared days after I put in a marimo moss ball. I have some questions regarding the outbreak.

- Is it imperative I clean the cyanobacteria from the tank as soon as possible? Or is it okay to wait the 5 days until my schedule cleaning?
- Does the marimo moss ball have anything to do with the sudden outbreak of the cyanobacteria?
- Is cyanobacteria harmful to me?
- Does it do anything but be unappealing to the eye? (I assume it does, but I am wondering what)



Fish Guru
Jan 26, 2008
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Perth, WA
Cyanobacter bacteria are a photosynthetic bacteria that loves light, nutrients and minimal water flow. They can live in fresh, brackish and salt water, and come in a range of colours including blue, green, black, brown, pink, red & purple. They do cause skin irritation in people, animals and fish but normally require direct contact with the skin to cause this. They can poison animals and people if you ingest it. Washing your hands and arms with warm soapy water will remove it from your skin and prevent irritation.

In an aquarium that has a heavy infestation, fish (usually bottom dwellers) can develop skin rashes and sometimes die. Fish swimming in the water column are normally unaffected but can still have a few issues if the Cyanobacter cover everything in the tank. Some fish will eat it and are fine with it.

One of the ways you control or fix Cyanobacteria outbreaks is through daily water changes and gravel cleans. You literally try to suck out any that you see and physically remove it from the tank. If you leave it for a few days then it spreads and spreads rapidly.

Increasing water movement, cleaning or removing any organic matter from the tank (using a gravel cleaner daily for a couple of weeks), reducing dry food going into the tank, and making sure the lights have a Kelvin (K) rating above 4000K should all help.

The Cyanobacter bacteria probably came in on the Marimo ball.

It can smother and kill aquatic plants.

It sometimes occurs in newly set up aquariums and goes after a few months when the tank becomes inhabited by more different types of bacteria, viruses and algae. But try to get rid of it asap.

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