Cyano bacteria.
Usually the main reason for Cyano is overfeeding and old lights. I personally feed once every other day in a controlled amount. What kind of lights do you have and how old are they? If PCs get old, the light spectrum changes and promotes a lot of unwanted algae growth.
i have 260w pc lights from orbit had them for a month now. how much shouls i feed for 2 clowns and 1 damsel. i feed teem formula one everyday and prime reef every other day
Feed as much as they will eat in 2 minutes, once daily.
What do you have for filtration? What are your nitrates and phosphates? Do you use RO/DI water? What do you have for circulation? How big is the tank? How old?