So I have a 20g long, cycled, with two 60g HOBs. No live plants.
Inside lives one little oranda goldfish who seems lonely now that his friend (also an oranda) has passed.
I don't want to do another goldfish because I think that's just too much big fishies in a small tank. As it stands we'll probably upgrade to a 29 at some point when money is less of an issue than it is currently.
But he does seem lonely and bored. I was thinking of some smaller fish for him to swim around with to at least provide some entertainment. Originally I was thinking of guppies as they don't up my stocking too much, even with 3. But I don't really know much about them in general. It's a stable tank with way too much filtration but good for the goldfish so I'm not worried about a water issue, just space and aggression. A 29 is in the future but not immediately.
I read that cories are good with goldfish but again, that's a fish I know little about.