jake - i feed my copperbands mysis and other meaty seafood. they have a difficult time learning to eat pellets and flakes, but not impossible.
sweetrav - marginalis and copperbands are nearly identical in behaviour. but marginalis butterflies, from my experience, are easier and feed more aggressively. they are peaceful and super reef safe. none of mine ever ate any corals. just tube worms.
update on my paucifasciatus butterflies pair. they're still alive and feeding very well on mysis and pellets. i will get to see them in 16 days!