All the fish in your tank will eat the snails. Don't add a new fish it will only add more bioload and disrupt the dynamics of your tank. Plus, most snails are harmless. People go to great lengths to get rid of them and waste time, money, energy for nothing. Snails are really hard to get rid of once they get established. Your best bet is to set traps by using an empty bottle with bait and leaving it overnight. In the morning just remove it with the snails inside. Feed less and make sure there is not leftover food. Between this and your fish eating them they should disappear or their numbers stay low. Another thing, learn to accept the snails. I don't know why people freak out about other life forms in their tank and think they can keep everything out. Despite out best efforts it is a part of fish keeping that we need to get used to. And the snails are more beneficial than harmful; they break down waste and eat extra food, become natural live food for other animals/fish, and they are cool pets themselves. the ONLY negative about them is they look bad when there is like a 1000 of them on your glass. But you should never let it get that way if you do a good job in maintaining them. People suggesting to buy fish or use chemicals are giving horrible advice. You are keeping animals (fish), that live in water WITH tons of other organisms. I personally like the diversity in my tank and you can't keep your tanks absolutely perfect it is impossible.