is tropical fish food bad for a fantail goldfish?
It isn’t that it is bad for the fish in that it is poisonous or anything like that. Tropical fish food just doesn’t have the proteins, etc that goldfish need. Goldfish are a coldwater fish and thus they have different nutritional needs from tropical fish. Feed it a good quality goldfish food (it will say right on the container that it is goldfish food) and supplement with treats once a week or so. The treats could be freeze dried or frozen baby shrimp, bloodworms, tubifex worms, etc. Most fish love, I mean love, bloodworms.