It also could be a problem that the other softies are releasing chemicals into the water to inhibit growth of other softies. I had this happen before with 2 soft corals. They both started out about 5" high, then they both grew to about 18" high, and then one shrunk down to around 2" and dwindled away from there. I attributed that to the other coral releasing stuff into the water (might not've been, but water parameters checked out, and couldn't find any problems, so elimination led me to that conclusion). Try adding some carbon and see what happens. Or, it could just be the adjustment period like everyone else said.