Kuhlies and most other loaches eat snails but a lot of loaches, clowns for example, grow quite big.
56l = 12g, so I wouldn't recommend any loaches.
You can often entice the snails onto a bit of romaine lettuce or kale then you could put the snails in a tub in some water, put that in the freezer and that is a more humane death for them than pouring them down the drain or killing them with chemicals. Personally though, I just leave my snails as I quite like them, and couldn't bring myself to kill them.