Thanks so much for the input, unfortunately I think it is to late. Fish was looking pretty lethargic so I wanted to get it out of the copper. I put it in the sterile tank with no copper and it was way skinnier than I thought. I thought the fish was eating a bit in QT but it must have not been near enough. Pretty much gave it up within an hour or two. Pretty bummed out, started with QT'ing 3 cardinals and all three did not make it. Thought this was the strong one as it was active yesterday and at the very end of Copper, Metro and GC treatments. The little I did see them eat must not have been enough. Feels like a waste of life, money and time...I really thought I was doing everything perfectly, seeded the sponge from my tank for a month, ammonia was always 0, lots of aeration, copper was going well with the Hanna checker. Do must fish eat decent while in QT? I feel like that has to be what went wrong.