Well, from my experience, I have kept my 3 goldfish for last 2 years at temperatures between 74 to 78, sometimes even hotter in really hot summer days, with tropical fish, and I have had no issues with anything. My gold fish are as colourfull as ever and so are my platy. I kept gold fish when I was in India. There the water temperatures never got colder than 75 deg even in winter. I used to have 2 fantail goldfish with 2 red wagtail platy in a 10 gal, and I got a 3rd fantail from my friend few months back. Now the goldies have outgrown my 10 gal and I plan to move them to a 20 gal.
I want to keep the water at the same temperature. I am looking for fish who will not nip at their fins. Any suggestions? I dont want to restrict myself to cold water fish. I really love the german blue ram! But all fish compatibility sites say that goldfish are not compatible with other tropical fish! Even though I have kept mine with others always. Can anyone help me with information regarding compatibility with the GBR (other than temperature)