Add a pair, if your living the damsels in there, you may want to make sure the pair is a larger one. Also since you have the damsels you may want to add a spieces of clowns that is a little more aggressive.
However, since ever fish is different you may be okay with the damsels and clowns together. Or they may kill each other. Just watch the fish after you add them and don't put in two really small ones.