In one of my community tanks that's a few months old I added a true freshwater puffer. He is only about half an inch long. Since adding him a week ago all but my neons and the puffers fins are nipped. Is it the puffer like I suspect? I can never catch anything in action.
If no one was nipped much beforehand, then it seems like it must be your puffer. I don't know a lot about them but I think I remember reading that they can be pretty aggressive and aren't good for community tanks.
Most likely it is your puffer. Is it torn fins, or bit fins? I noticed that when my fish picked on each other, their fins got frayed or ripped (like an overused flag). However, when my puffer got a hold of my other fish, it wasn't like that. It was like there were little half-circles missing from the edges of their fins. Neat, little puffer bites.
I'd suggest a species tank for him, if he doesn't eat them now, he will later once he matures.
I just read that link meenu, thanks! Wow such a little terror. I was foolish buying him, it was an impulse buy since my fav LFS has never has them till my last visit (of course I was told he would be fine in this particular tank). I don't usually trust the lfs advice but this particular store is pretty reliable.