JeffL, i realised you seem to have this problem... like getting harlequin shrimps without knowing they eat starfish, clownfish not feeding etc. If you read a bit more before you purchase your lifestocks i think you will benefit more.
On buying fishes, try to ask the LFS to show you if it's feeding. Usually they have some pellets etc on the side of the tanks where you can feed the fishes to see their response. Always good to get those fishes that are already feeding, as non-feeding fishes usually won't do well at home as well. Also, you can get the same food to ensure at least there's one type of food they eat before you throw it others.