Might just be too busy of a food for him. There’s a bunch of different proteins and both peas and potatoes. Maybe try a limited ingredient food. Like natures variety limited ingredient or merrick limited ingredient. Or maybe even the merrick classic foods with grains. Those aren’t bad and better for dogs who maybe can’t handle all the peas and potatoes and really high protein. I would only try feeding it for another week or so. If it isn’t going to get better by then it probably just never will and that would just mean he isn’t going to do well on it.
