This a problem ??

[Diana]

IME, it is high nutrients that cause cyanobacteria. Using carbon along with other nutrient absorbing filtration media(like phosphate remover) will help, as will testing your nitrate levels and doing small frequent waterchages as neccesary.

Sometimes also, cyano is a stage that quickly passes as other living organisms in your tank outcompete it for nutrients, stuff like macro algae, microalgae, even corals.

HTH a bit.