Another thing, loose stools are sometimes a side effect of antibiotics and other medications. I know that at least with one of my dogs an antibiotic had to be changed to another due to side effects.
So, the diarrhea may not be related to his diet.
I think a call to the vet is in order. Leave a message for him to call you back when he has a minute. There are some good vets out there, and they don’t mind returning phone calls to answer questions especially if you frequent the same veterinary clinic.
I found out that was the best way, find a vet that you trust and listen to him.
