How old is the tank, as in how long has it been set up as a saltwater? If less than 2 months it could be a diatomaceous silica algae bloom. This is normal and should clear up. Are you talking about long hair like algae? I hope it's not really a red cyano bacteria.

Old bulbs can lose their spectrum. Lost spectrum creates more yellow which algae thrives upon. Yellowing bulbs can cause good corals and such to quit growing which frees up nutrients for algae to feed upon. At that rate algae will out compete other higher forms of life.

Do you have a refugium to help absorb and export excess nutrients?