Having a snail in your frog's tank can actually be beneficial as long as it's not overrun with them. The challenge is to keep the snail population down as they reproduce quickly. However they do clean the tank by eating leftover food and decayed material. Unless you clean everything you place in the tank, you will find that snails appear eventually. Don't use snails from your garden or neighborhood as you don't know if they carry unwanted bacteria. Purchase the pet shop variety.