Mantis, obviously you didn't read their signature. A clown loach will NOT be suitable for two 1/2 gallon tanks or a 5 gallon tank.
I myself don't know much about killing snails but I know that you can stick some lettuce or something in the tank before lights out, and then in the morning when it is covered in snails take it you. Of course you will never get all the snails. Just reduce your feedings and the snail population will diminish.