Just to mention, my entire fish population has been in a 100 gallon tub with CP for the past month with no issues. I have 4 tangs in there, cleaner wrasse, leopard wrasse, chromis, 2 fairy wrasses, flame angel, 2 clowns, banghai cardinal, and a dartfish.
It seems pretty mild to me on the fishes but I do believe it does lower their immune system as in have to keep an eye out for bacterial infections. When used as a malaria drug in humans, a side effect is immune system suppression so I'd imagine the same in fish.