Chromis get too big for a 20 gallon no?I heard Damsels are aggressive. A good alternative is a Green chromis. I picked one instead of my initial choice (which is a damsel) and I'm glad I did. He never gets tired of schooling with my Clown pair and they are best buds together in the tank. The chromis wont follow anyone else but the clowns. Sorry for being off topic but thats also an option you can think about.