Stocking tank question!!

[Adam Mac]

Ok heres what happened. I bought a firefish put him into my tank and instantly my powder brown was like a hammerhead shark around this firefish. Next thing you know hes chasing him and the firefish jumps out. So I had problems. Tore down the tank last night got my powder brown out and in my sump for now. I have another firefish coming today. Question is....with the tank being completly different from when the tang was last in there. Now i put the 2 firefish in maybe leave them for a few days let them get settled then put the powder brown back in. Is he going to act the same or will he go back to how I original got him which was a normal reef safe fish. Can anyone help me out or maybe someone had the similar thing happen to them. Any input would be awesome.