Mystery snails eat diatoms, but they don't clean it away! they leave marks :P
I can sel you mystery snails if you want, 5.50 shipping, and $1 for the snail. You can even have more than 1 per box if you get them young. If you don't want the babies, crush up the eggs and feed them to the fish (my tetras LOVE them) you need more than one to reproduce though.