My friend has a really nice aquuarium. It is rather small at 15 gallons but she has a great pump and its well decorated. She only had one goldfish for 2 years and it is getting crusty stuff over its eyes and it starting to bump into stuff and her birthday is next month so I thought to myself "I'll buy her a couple fish" but NOTHING can live with her goldfish according to my research so I decided I will just wait and see how her fish does and if it dies =[ then I will buy her a different kind of fish. I don't think her current aquarium has a heater but I could get one if needed and yes I am researching the nitrogen cycling stuff because it seems to be posted everywhere on here but what kind of fish could live together and how many smaller fish could a 15 gallon support? I'd like at least 2 fish max of maybe 5 which seems kinda high and of differing varieties if possible. If not I will just default to goldfish.