Hippo Tang with ick

Hi!, my upgrade to a 75g was successful, the tank has been running for more than two months, lost no fish or corals and tank is thriving. I bought my hippo tang in july and it was doing great , I feed a variety pellets, flakes, frozen, and seaweed and fish was healthy. About a month ago I noticed ick on the blue tang and yellow tang, the cleaner shrimp is on my yellow almost every night so the ick would be gone the next day, but the shrimp doesn't bother with my blue tang, so he would just get worse. It would come in waves, and right now its at its worst, and looks to be more than ick maybe something fungal? I did my research in HILLE ( not sure spelt correct ), and stopped using carbon total, because my tang also was loosing color around its eyes. It has gotten to the point where expect to find a dead fish in the morning. I have corals and shrimp in my tank so I've never consider copper treatment, but now I feel I have too. I set up a 20g system and is ready to go so I can treat the fish, problem is there is no way I can catch the fish, and I do not want to stress hippo tang or other fish while trying. The tang sleeps wedged in rocks and taking down rocks is not an option, I would have to move to many corals and this rock is a support rock and can't not be moved without a disaster. And ideas on fish traps? I really want to bring my hippo back to health and would hate for it die, I know there is reef safe options, but I simply can't spend a lot of money on treatment that needs to be dosed weekly and restocked. And my concern is that treating with copper in the 20g will basically mean the equipment on 20g can't be used for my reef? For example I have live rock in the 20g will the rock " absorb" the copper and potentially leech out if put that rock in my main tank? I don't want to cross contaminate with the copper. Any suggestions thanks!