Depending how big your pinch is, you may be underfeeding your tank. Reef fishes can put away a surprising amount of food. If your Angels, Tangs and Wrasse are properly fed, their stomachs should be obviously rounded, but not overly so. Definitely not concave like in the picture of your Firefish.
If you found your Firefish beat up immediately after the blackout, I would suspect the aggression was brought on by insufficient feeding.