3 female bettas would work. pair of breeding gouramis. I don't feel to bad about your discus as those fish are very slow. although they probably will never reach dinner plate size, like prize quality discus. I wouldn't put a comet in a 10g for 5 years tho. like I said mine are all 7 inches thats half the size of a 10g. They are very active fish. But I encourage you to watch your nitrates so you don't stunt any of your fish. once a fish is stunted it will never grow the same again.