My 5 year old sibe had the same problem, he would have hard stool one day and the runs the next. I kept switching his food for about a year before someone told me about Evo red meat. He did great on it, and I switched him over to Timberwolf Organics. My new 5 month old pup was on Wellness puppy food and she had the runs too, I switched her over to Orijen Puppy and she's been doing great. Evo red meat, timberwolf organic and Orijen are all grain free..maybe your pup would do better with grain free food.