What you can do if you have some time, cut little slits in a water bottle and put an algae wafer in there over night. Do this for a few nights and they should all be gone. I had removed almost all of the snails this way.
Once you see eggs on your plants or glass, then that's when you're going to have a problem. I was considering getting an assassin snail to rid them, but my "snail trap" proved useful.