Have a Powder blue (healty - no whitespot or anything else and he has been in my tank for three weeks now) and a (small) regal in my display tank. Problem is that the powder blue has taken a serious dislike to the regal. All was OK originally but for the last week the regal cannot show his face without being seriously harassed by the powder blue. Is this usual? Also have a relatively large) yellow tang and a scopa tang in my tank and, aside from the occasional show of power by the yellow, all seem fine with each other.