I put in an apple snail, and trapped the rest. The apple snail will eat the eggs of other snails, and sometimes small snails too. Of course they are also likely to eat all your plants as well.
Snails are easy to trap. Drop in an algae pellet, wait a couple hours and it will give covered with snails. Just scoop them out. Repeat once a day and the snails will be gone in short order, or at least down to a managable level.
Loads of snails is also an indication of over feeding, so check to see that you aren't doing this.
Most any chemical that kills snails kills shrimp too.
You could also try putting in a piece of cucumber - my shrimps love to nibble at it and the snails love it even more - and once they are al firmly attached to it - you just remove the piece of cucumber