PBT is not a easy fish, and if I am not wrong, u used salt mix to cycle the tank. From my exp, salt mix cycled tank need a long time to stable down. my 1st tank and 3rd was nsw, never cycle, none of my fishes died inside due to tank crash, 2nd and 4th tank using salt mix, even after 1 mth of cycling, newly brought fishes were easily stressed up.
I lost alot of fishes in the past because of no QT to cure fishes. If possible, set up a QT tank. I notice fishes tend to be more relax when they are alone in the tank.
Powder series tang are almost 100% on getting white spots. It doesnt matter if u add in the pbt first or last, at least that few hrs or 1 day dont make any diff. that happen to all my powder series except for a hybrid pbt. I left it alone in a 4ft tank without chiller and lights for 2 mths. no whitespot breakout.