Coldwater Fish In Freshwater Tank?

I posted my thoughts in the general area

The main problems are that goldfish get VERY large and require a higher water oxygen level than tropical fish. I have treated ich on goldfish with the salt bath and they weren't affected. Believe me I want to put a goldfish in my 55 tropical as another scavenger, but they are incompatible with angelfish.

I think the "disaster" forecasters overstate the case a bit. Like everything else, it depends on specifics. Goldfish can grow rather large, are fairly heavy bodied, and can put a strain on your water chemistry. They also tend to do better in rather cooler water than most of the popular tropicals. The #1 question though, is what do you have in your community tank? Many tropicals will "pick" at goldfish -- both the fins and the body slime. This results in a lot of stress, and often leads to disease and death. Some cichlids will just kill the goldfish out of hand, particularly the fancy varieties that aren't very mobile. All in all, it's probably more risky than it's worth, but if you want to try it go ahead. Just be very watchful, and don't toss your "coldwater" tank just yet. It's likely to be a "learning" experience.