For starters test your water if your having this big of a problem. Especially nitrates and phosphates if these are out of whack fix them. If your algae is in big sheets, you can remove some of it by hand (this would be the blue gren type that actually is alot of times not blue green in color at all). Also how much light you're giving may be a factor. Last but not least, if you don't already have them, get a whole bunch of algae eating critters. (I must say I'm particulary fond of the packages this site has put together) They make it so simple to get exactly what you need! Good Luck