A lot of people swear by otocinclus catfish, which reportedly mow down diatom and soft green algae. I've never had any, so I wouldn't know. They won't work on that hard green algae that is flat on the glass, though. I occasionally feed mine sinking hikari algae tabs, and they seem pretty fat and happy. They also seem to poop in spurts, sometimes not producing much for a week or more. When they do, they create a fair amount of it.
