Can you keep coldwater fish (Goldfish, Shubunkins etc) in a tropical aquarium with a heater?
Absolutly not, some fella asked this back along, its crazy, they are called coldwater fish, therefore never put them in a tropical tank, I have Discus fish who have to have perfect water conditions, the right high temperature and reverse osmosis, you’d never put these with Goldfish, go ask your nearest fish specialist, anyone on here who says otherwise is having a laugh, they must have the luck of the gods if they are trying to tell you that they have these fish living together in harmony, buy books on it if you need to, I told my father about this the other day, he’s extremely knowledgable in this area and couldn’t beleive that people honestly think coldwater fish can mix with tropical fish who need specific water conditions. Put goldfish etc in a separate tank, hope thats enlightened you.