i just finished dealing with the same problem.....
it took a mulit stage process!
i would cut water bottles in half(long), out a bunch of algae wafers in, and wait a couple hours, the snails load in, i took the bottle out and dumped it into the pea puffer tank. he'd suck them right out. I filled, no kidding, atleast six bottles worth to get it to a reasonable state.
I the got a couple zebra loachs, and they finsihed the rest of them off nicely.
i did a bunch of research try'n to solve this. other known snail eaters.
Loaches generally, theres a couple that don't, but most of them eat snails to some degree. shell doesn't matter, they more suck them out
Pea puffers are great too, depending who else is in the tank, they also suck 'em out.
sparkling gourami's, known snail eaters, although fairly un agreesive, they work well in a matinence programs
thers some more i can't think of right now too....