lifeoffaith
Member
I have eliminated a pretty bad cyano outbreak by washing the pieces of liverock it was on with freshwater, and also limiting light. Of course, you can take out some of the good stuff by washing with freshwater. I know this can be easier said than done if the rocks are on the bottom of the tank or if it is on the glass. I have also kept it in check by siphoning as suggested above, but I can't answer the why question you asked.