All marine animals are sensitive to abrupt changes in their environment, so stability is very important. All butterfly fish are sensitive and their rate of longevity is not much in captivity unless their needs are given to them. All butterfly fish eat coral. Some are more specific, some others feed on variety of coral. Copperbands eat aptasias and are beneficial in any tank with live rock. They rarely bother other coral, but will nip at small polyps and sponge, feather dusters maybe. Raccoon butterflies are one of the hardier species as well as the copperband and not so demanding in diet, but even with them, their longevity is cut rather short in captivity. I personally believe butterfly fish are best left in the ocean given their needs are rarely ever met in captivity. They have to have coral protein in some fashion. There is butterfly foods that contain sponge and helps them live longer.
Make sure the tank is well matured...at least six months to a year and that the water parameters remain stable and the system, pristine. I'd never house a butterfly in a fish only tank without any live rock.
We, as a people, know so much more about outer space than we do about our own oceans. This lack of knowledge can very well spell the dangers that lay in wait for us.
The oceans surely would swallow us before a rock comes down to smite the planet of it's life.