Okay, it sounds like we need to make a list of the tried and true methods for making fish happy and friendly:
Allow the fishes natural food to grow in the tank for weeks or months prior (Macroalgae for herbivores; bugs for carnivores);
Set up aquascaping with areas that closely approximate the fishes natural hiding places;
Feed as much as the tank can handle for at least two days prior to introduction;
Pick full bellied fish that are active and if multiples, are hanging out together;
Politely thank the LFS for their advice, but check here to confirm the truth or call me right on the spot at the number below;
Take multiple fish home in the same bag, where feasible;
Use an acclimation container for several days or even a week (Be prepared not to release the fish if bad vibes or aggressive displays do not stop.);
Remove the tough guy until after the new fish have made their home; and
Train the fish to get along. You are the "Alpha".
I realize that some people think I am just plain crazy to suggest this fish training thing, but it really works. See the Reefkeeping Tip for a detailed explanation.
Aloha,
Mark
808-345-1049