snails will eat algae wafers. Another decent alage eating snail is the Malaysian trumpet snail. They are nocturnal, and live in the substrate...so even if they 'infest' your tank, you won't see them unless you turn on the lights at night.
Otos really are the best for eating the green stuff on the glass...maybe try them again when your tank is more established?? They are hard buggers to keep alive in the beginning, but once you find some hearty ones they'll take a lot of abuse. I usually buy 2x the amount i want to end up with.