Yes I have tried it in the past. It actually works really great (in my opinion) but only 2 or 3 fancy goldfish would work. Too many and the discus wont get food and the tank will be filled with goldfish poop. I personally don't believe goldfish can stay only in coldwater. I think they can adapt to a very wide range of temp. I don't like keeping discus with goldfish just because it looks weird (to me).