it would help if there was a picture. Different herbovoires eat different kind of algae. Some tang speices...kole, chevron, yelllow...eat green algae. I have a hair algae problem, just ordered 60 snails for my 75 and its really getting better. That and an urchin. The urchin can cure a whole rock in a night itself. get a good algae eating cleanup crew. Depending on which species of algae, a foxface, lawnmower blenny, and tangs could help too.