Gonzo was started on Purina by his owner, and I bought a huge bag. His stool is now...rather soft, not quite diarrhea, but not looking normal. The vet gave me a sample bag of Science Diet I might start mixing in. I gave my Yorkshire Terrier Science Diet her whole life and she never had problems, but yet I hear they changed the recipe and it's not nearly worth the money as it used to be. Purina seems like a cheap brand--should I switch to something better? He's about 10 weeks old.