Although it is frequently called algae, Cyanobacteria is an especially ancient form of bacteria which happens to be able to carry out photosynthesis. As such you can eliminate it by depriving it of light or dissolved nutrients. I have also had success by treating it with erythromycin, which kills it off in a day or so. But as one of the leading members of the "take your time" school here, I would recommend manual removal when you can, lowering the nutrient level in the water and lights out for several days. This too shall pass!
