Excessive fish waste, over feeding, overstocking the aquarium, low oxygen, and a lot of light will help you grow algae. Which is everything you shouldn't do. HA HA. If you've had your tank set up awhile then it appears your algae eater is doing his job well. My tank was overstocked with goldfish (which I Absolutely LOVE because they are indestructible no matter what I do to them) and I put in one big algae eater and never had the problem again. If you think your algae eater isn't eating enough you can always buy algae wafers for it.