Hardly any tang is peaceful to newcomers once established with perhaps the exception of hippo tangs and even they flash and trace. small and less aggressive fish need to come before tangs. To answer the question I had to take my powder brown tang out the display tank for a week when I added my anthias and midas blenny. he would have killed them or stressed them to death had I not taken him out. I knew it would probably happen and already had a tank to put him in. I did just add some false percs but I completely reaquascaped the day before. that worked well but only works if you do it BEFORE you add the new fish. you add the new fish and it gets chased you can move the rocks all day long but I wouldn't get my hopes up of it working. you are probably going to have to remove the tang for at least a few days and reintroduce it. might want to wait longer just to be sure.
