Goldfish help

[Jerome]

Hi, I don'tsuppose anybody knows about Goldfish? Only my stupid sister thinks they are some kind of toy .. some novelty act that cleans and looks after themselves and so now one of them has "swim bladder" I think .. it's floating at the top of the tank upside down .. not dead because it swims (or tried) down to the bottom sometimes before floating back up like it's got trapped air.

How do you solve it? I mean .. it had it the other week when I cleaned the tank out and after I put it back in it was OK ... any help