Peter, I'd highly recommend making yourself a "butterflyfish feeder". I'm convinced it helped me keep this Long Nose Butterfly for over 7 years.
I simply drop in a cube of food and it allows my butterflys to pick for an hour or two, depending on the type of food. This is simply the clear intake tube from an old Powersweep powerhead. (the only thing those powerheads were good for).
<a href="http://s374.photobucket.com/albums/oo181/phil_1975/?action=view¤t=LNB.jpg" target="_blank"><img src="http://i374.photobucket.com/albums/oo181/phil_1975/LNB.jpg" border="0" alt="Photobucket"></a>
I recently added this Copperband but initially he wouldn't swim to the top of the tank to feed from the feeder like the LNB would so I temporarily rigged up another tube feeder lower in the tank and he quickly figured it out.
The Copperband started with clams and shrimp but now eats any frozen food I put in the feeder. The LNB always ate any frozen food I put in there. I feed a combination of Ocean Nutrition cubes, Rod's Food, PE Mysis and slivers of frozen scallop. They are eagerly taken. The only downside to using Rod's Food or PE Mysis is that as it thaws it sometimes floats out of the feeder and other fish snatch it up.
<a href="http://s374.photobucket.com/albums/oo181/phil_1975/?action=view¤t=CooperCyrano.jpg" target="_blank"><img src="http://i374.photobucket.com/albums/oo181/phil_1975/CooperCyrano.jpg" border="0" alt="Photobucket"></a>
Both butterflys are fat and healthy even with the world's greediest naso tang cruising the tank. They would never survive long term if they only ate from the water column. In fact they're so conditioned now that when I drop loose food in the tank they'll immediately swim over to the feeder expecting a meal.