Presumably he (or she?) wanted to go back to his own tank to get the regular food. Frankly I think you should take the carpet down - OK you don't want to keep losing flounder, but if the guy can wander around and climb out of his own tank you should be studying that, not trying to make the behavior go away. If nothing else, it's cruel to bore him like that. Yes, I'm serious.
That might be something that you would want to try in a research aquarium, but sadly a lot of aquariums are more for human entertainment, than for study and preservation of species.
