I swear that I have a Frontosa 5" female with some African cichlids and four feeder goldfish in a 100g. It's not my prize tank of course.....the feeders were survivors from a terrapin pond and they are 9 years old and 4-5". They don't get bullied and I didn't know what to do with them. They live in harmony so I never pulled them out. I do have 2 filters for the dirty @3$@/!!! Fluval fx5 and a 405 kinda overkill but it screams like a river and its way clean. No success with plants so nitrates suck to manage. But yes it can be done but I don't suggest putting goldfish with anything. They can carry diseases and are way dirty.