I don't buy the whole you can't QT copper bands. I have QT'd a few myself and they took it fine. I wouldn't cut QT short and hope for different results in the display. The risk to my established fish is too high. Some things to consider. How often are you feeding? With finicky feeders I like to hammer them with food. I will take a slurry of every frozen food and dry food I can get ahold of and add a small squirt hourly or 10+ times a day until they are eating well. I love mastic after using it to get my Prognathodes to eat, I like to mix it with a frozen, food, usually an angelfish or butterflyfish prep with a large variety of ingredients, or something like brine or mysis, and smear it on a rock. Live foods are fantastic to trigger a feeding response, be that brine or worms. It's fairly easy to hatch brine at home, so that could be worth a try. Dither fish can also be helpful, like a black molly, or another docile fish. I sometimes will add a clump of macroalgae from my sump to the QT to provide a source of pods, for the fish to snack on. I like to have a ton of cover in my QT tanks, be it live plants, pipes, or other inert decorations, to give the fish plenty of area to explore and hide. Few things to consider and try before possibly introducing pathogens to your display.
Mine went on various hunger strikes throughout but did just fine in quarantine. I did quarantine him with another fish. Maybe that helped him feel more normal. Best thing you can do which ever way you go is to make sure the fish is eating Before you buy it.
