Well, first things first, identify the algae, that will help you determine how to treat it. After that, I'd take a look into why the algae grew in the first place. Most often it is overfeeding combined with too much light. What more can you tell us about your tank? Ammonia, nitrate, nitrite and phosphate levels would actually be pretty helpful. What sort of filtration do you use? Does the tank get any direct sunlight?