The two most common types of red slime we encounter are – cyanobacteria and spirulina (a type of cyanobacteria).  These are very different and require different treatments.  Never treat anything in your tank until you have positively identified it.

How to identify what type of red slime you have.

1. The cell structure for each looks different under a microscope.

Spirulina Red Slime Under a Microscope

Cyanobacteria Red Slime Under a Microscope


2. The peroxide test.  This is typically the easiest test to perform since most don’t have a microscope.

a. Remove a good sized chunk of red slime and put it in a container along with two cups of tank water.

b. Add 1ml of 3% hydrogen peroxide and let sit for a couple hours.

Cyanobacteria reacts to peroxide and spirulina does not. If the slime sample or water has reacted then you have cyanobacteria. If there has been no reaction (the water and/or slime sample will generally turn a pinkish color) then you have spirulina.


Red spirulina – Chemiclean seems to be the go-to treatment.

Cyanobacteria – Dose peroxide, start with 1ml per 10 gallons.

*** Yes, I know the chemiclean package says it treats cyanobacteria, but it doesn’t differentiate what type.  I believe Boyd’s is using the term “cyanobacteria” as a general term for red slime.  They are counting on you (the consumer) to be uneducated and they’re OK with you wasting your money on their product.