During the copper treatment, the tank because a quarantine tank, so it is the best time to add new fishes and rethink the type of fishes to be added.
Top Tank:
It basically contains tangs. I have Yellow Tang, Brown tang, sailfin tang, BPT and clown tang
Bottom Tank:
It also basically contains tangs and triggerfish. I have Blue Tang, Powder Brown Tang, Epaniette Tang, and Naso tang; Picasso Triggerfish, Undulate Triggerfish and Niger Triggerfish.
None of the fishes have died after the copper treatment.
Ich will only only come back if there is new sources such as from the NSW and new fishes and corals added to the tank, so you need qt the fishes or coral for 3 weeks before added to the tanks.
I use fresh water to drip the red bamboo ( food for the tangs) over night to kill the ich before putting in to the tank. Not sure freshwater will kill the ich, until now it seems to work.