Remedying a snail issue with fish that eat snails is almost never a good solution. Assassin snails are an option, but keep in mind that these fascinating critters need a steady supply of snails to eat. If you get a few and they manage to wipe out the entire population, you should consider finding them a new home.
Your best bet, as mentioned in above replies, is to physically remove the snails yourself. I have found that the best method for this is to sink a large piece of vegetable, such as a leaf of lettuce or a slice from a big cucumber/zucchini, in the evening. The next morning, before your tank lights come on, remove that vegetable. In horrid snail infestations, the veggie will be completely covered by morning. With smaller amounts of snails, you may only see a few each morning.
Removing them first thing in the morning prevents the snails from having their dinner and then crawling off to lay eggs. When there is an abundance of food, their bodies are triggered to begin reproducing rapidly. It is not unlike the concept of supply and demand. To prevent an infestation, be sure that there is no uneaten food laying around the tank aside from your bait.
