Well, judging by that pictures, you've got the Purple Psudochromis alright. Pseudochromis porphyreus if I remember correctly. Pretty, but mean little buggers. You can help cut down on aggression by making a lot of caves out of your live rock, as that's where he'll hang out mostly. I would worry a bit about aggression between him and the melanurus, but it shouldn't be too bad once they get used to it. I feel like there may be some issues a bit later on though. I think the Melanurus may start to outgrow the 30, and that could maybe cause a problem or two.