Like GSP is a very good description which describes what ist is known as Green Turf Algae. They are coarse, wiry, and generally have thicker wider blades than Green Hair Algae. They may or may not have a mat like root structure, sometimes they just seem to sprout from the rock. Turf algae that sprouts directly from the rock can be a pain to control, as it is difficult if not impossible to pluck it all. Once discovered it should be treated outside of the aquarium, perhaps by dipping the affected rock or frag in water treated with an algaecide or even hydrogen Peroxide.
Turf algae that grows with a root mat can be peeled by pushing down on the algae as you scrape your thumb against the rock dislodging it in one swoop. Let it get big enough so you have leverage. Scrubbing with a stiff toothbrush or auto detail brush will also help. After youve cleaned it, add some: Pin cushion urchins, chitons, and even emerald crabs (although I dont trust emeralds).
