If you have decided to change his food, please make sure you do it gradually, as to not upset his fragile digestive system.
Maybe 1/4 of the new food with 3/4 of the old food, for a few days, then go 1/2 and 1/2 for another few days, next do 3/4 new food and 1/4 old food and gradually ease into the new food.
