THanks for the advice, you are probably right. In fact, when I feed them FBS, all the fishies enjoy it equally

I'll have to try cutting the bloodworms smaller, too
EDIT: on second thought, when I think about the flakes I'm feeding them: I've seen numerous times the smaller fish nabbing the tiniest visible peices, and they still spit it out! Another theory is that they are so spoiled with bloodworms and brine shrimp that they won't take flakes anymore! I guess I'm not fully convinced just yet.