What kind of snails? If you have an air pump, or can get a cheap starter pump with airline tubing and such... stick the snails in a bowl or bucket
I've done that.
It sounds like ich... you have AQUARIUM salt on hand? And is your heater adjustable? Get ready to up the heat once you see those buggers, and add 1 teaspoon per gallon (or a tablespoon per 5 gallons) of DISSOLVED aquarium salt. Daily gravel siphoning helps gets rid of the parasites from the bottom. The heat (84-86) speeds up the ich life cycle, and the aquarium salt dehydrates them.