We used to have African Clawed frogs in a community tank. We had the same problem: by the time the frogs figured out there was food in the tank, the fish had eaten it. We solved the problem with a 12" set of plastic tweezers that my wife acquired from her work. Physicians use them to remove objects from children's noses mostly, I think. Anyway, she used them to introduce mealworms, shrimp pellets, and other tidbits directly to the frogs snouts. Once the frogs discovered food, they quickly became adept at finding it fast enough to get it before the fish. They soon grew to nearly 5" and started eating small fish, so had to be moved to a different tank.