i don't know anything about puffers, but i know that ramshorn snails reproduce very fast and can take over a tank in a week. a lot of people [including me] think of them as a pest, but they would be good for a puffer tank.
Thanks for your advice again Diamond. I'll do a little research on the ramshorn snail. I remember reading somewhere that a type of snail is not good for a puffer and can actually break their teeth but I can't remember which one. I'm trying to find the article again. I'll probably start a separate topic somewhere to see if I can get some more answers.