Mattgoldfish. Go in and read my reply to the question of guppy nipping on lionhead. I have added a whole list of the gold fish groups. Your tank is way too small for a comet. They will get quite big. Could get to 7" or more. Please do not add salt to the aquarium. It will only kill the fishes. Salt is a big no, no to goldfish. Please go to the sight I have mentioned in the other question, and check them out. They will answer all your questions.