It's a really, really bad idea to add fish just to eat snails. Also, clown loach are just about the worst thing you could recommed as they can grow to over a foot long, and need to be kept in shoals of 6+.
The best method of snail control is a comination of trapping (with lettuce or cucumber; carrot is supposed to be good, but my snails won't touch it) and reducing feeding.