Why do people keep recommending fish to take care of snails? unless the OP actually likes the fish it seems the fish may end up wasting away?
Anyway, another method i've heard works is putting potato in the tank... supposedly they can't resist the stuff... also a good idea to put the potato into a net of some sort, so that in the morning you can lift the net with potato and snails out in one easy go...
Hopefully that will help you out at least a little, even if it means using up a few potatoes..