I have had fish that reacted differently to the exact same formula, based solely on color. As I recall they preferred the green over the red. Same formula, just different dyes to color the food. Fish can and often do have preference over pellets brands/formulas, no question about it. Sometimes it's as simple as what they were raised on, and used to. Frustrating to the owner that is attempting to increase the quality of the fishes food, only to have a stubborn fish that refuses to eat. I've trained a lot of difficult species, including many wild fish, and have always had good success by pre-soaking the pellets in the juice of frozen blood worms, and feeding sparingly once in the AM when the fish is hungriest. It definitely takes some extra effort, and sometimes the patience of Job, but in the end I almost always win.