I try and mix it up and feed every other day except for the meat eater tank. Our 55g sounds similar to what you have. Try a mix of Formula one and two with a bit of
frozen brine shrimp and everyone should be eating. Every third batch gets soaked in Selcon and garlic oil. I avoid flakes altogether as they are supposed to be the nutritional equivalent of Top Ramen.
For our meat eater tank they get a chopped up version of shrimp, scallops, fish, mussels and who knows what meant for human consumption at the asian food store. At four bucks a pound it cannot be beat.