Changing food multiple times with a young puppy is not the best idea but I do understand your concern. If the Wellness is not working perhaps you could try Pro Plan, (not the shredded variety), since the puppy was on a Purina product from the beginning. An adult fprmula is fine at this age. Many breeders feed and recommend Pro Plan and it works well for them. I would definitely not recommend starting the food rollercoaster at this age.