Your best sticking to a good quality pellet as a main diet. Then offering treat foods, say once a week. I use earth worms mussels prawns and I'v started using rainbow trout alot. If your umbee starts to refuse pellets then that's a good indication that your over doing it with the treats. I've had this with my fussy Dovii. I just starve him till he takes pellets again. That's how I do it. Others may have better suggestion.