The only think worse that not quarantining is bad quarantining! The smartest approach is to have a full cycled and established medium sized aquarium ( 29 gallons for example) set up and running as a half-way house for new arrivals. This MUST be a system that produces water as good as - or better than- your main show aquarium.
In the case of delicate butterflies, the first week of ownership will determine if the fish will acclimate or simply fail. And protein nutrition is very important during this time as a condition known as General adaptive syndrome is unfortunately well established within the fish’s physiology
. I agree with some others here that live foods are usually best to stimulate the feeding response. With this particular species, a combination of - a resident live rock ( for picking and stimulating the feeding response) and live foods are really helpful. You will see the shy copperband become quite aggressive in its determination as it picks at the rock, proving it is hungry but has no way of knowing what to eat in captivity.
Along with the permanent quarantine setup, you should have a permanent brine shrimp hatchery . It doesn’t have to be exotic- you can buy a simple base with aeration device, that a plastic soda bottle screws onto and uses a cheap vibrator pump for aeration and current to keep eggs suspended. It takes about 36 hours to have a two -three day supply of food.
Slowing over a two week time frame, you can mix adult frozen brine and cyclopzzz to the live/ frozen mix.
And finally you can open a live clam or mussel and let it sit on the bottom a few hours a day- the copperband and other butterflies/ difficult angels will also pick at it and get some nutrition.
Copperbands are my favorite fish but they are hard to acclimate. Make sure the belly is not pinched when buying them or you will have an impossible battle to fight. The fish should also have a very bright luster. If it is dull or matt looking as opposed to glossy looking, pass on the fish.
Very Best of luck, James P