As previously mentioned, I too would stay away from damsels, yes they are cheap and hardy but they're more than handful down the road. I made the mistake a couple damsels when I stared and I got rid of most of them except one, he's become so smart to fish nets and traps it's scary. But anyways, I would also stay away from purple pseudochromis and six-line wrasse as I think they fall along the same line as damsels, a lot of people don't think so but they can be just as aggressive. I say you give us more info on your system like zona322 suggested and I agree with the fish he said to start off with, being clownfish and chromis. But make sure they're chromis and not damsels because they may look very much alike