When all the tests came back negative I knew it had to be something else causing his runny poops. The easiest thing to change was his food. He was on Victor which is a good grain free food from the breeder but wanted to switch to Fromms anyway so I made the switch. When I did, the puppy food (pink bag) had chicken in it also but closer to the main ingredient. It was #1 or 2. Victor was further down the list like 5 or 6. His stool got worse with the Fromm puppy so I switched to Beef Fritta (sp) and he dried right up.
I hope this helps and keep us posted.