From FrugalReef

Green Algae is a generic term for anything green that forms a film over your glass and rocks. It's sort of like the "other" category for algae. There are innumerable types of "green algae" in the world, and the one thing they have in common is that most people don't like it living on their aquarium walls. Almost any kind of snail will eat this algae, but you'll still end up scraping it off every day.

[edit] See Also

• Algae Control
• http://saltaquarium.about.com/cs/algaecontrol/l/blpicalgaediato.htm - Pictures