I'm with dragonforce. With your tank size, another mandarin and a couple of six-lines would be great for your issue.
My six-line did get aggressive toward another wrasse and killed it but the other wrasse was introduced well after the six-line was established. You'll be adding them as new members. Besides, the little buggers are only 1"-1.5" long. I think they could find some room in your place. VERY cool fish also. Love mine!
dual 175 MH
w/ dual 32W PC