Quarantine fish? In my experience, will make the fish condition worst.
Cause normally quarantine tank is small and don't have good filtration system. Feel that it will stress the fish more.
I even tried putting in a yellow tang. Ich full around body on 3rd day in the quarantine tank. Then I put it in main tank in those acrylic container. It recovered a little and I releaes it before fully recover, it still struggle through Ich attack.
So agree with the rest, most important is that it MUST eat..