why wouldn't you want to add fish to get rid of them? a chemical wouldn't get the source of the problem any better then adding loaches would. the problem is they were introduced into your aquarium, and there isn't a way to solve that now that they are there.
your best bet would be yoyo loaches or clown loaches depending on your tank size.
don't use chemicals as they kill the snails perfectly fine, but then you are left with hundreds of dead snails foulling up; your water and sending your ammonia/nitrites/nitrates sky high.
if you ABSOLUTELY would have to use chemical warfare, place a piece of zuchinni in at night and pick it out in the morning with all the snails on it, trying to get out as many snails as possible. then use the chemical and be prepapred to do daily LARGE water changes until the snails are completely done rotting.
believe me, its much simpler to get 3 yoyo loaches and let them go wild, then return them to the store 2 weeks later with your tank being snail free.