Loki is a 1 year old GSD that has had diarrhea for 3 weeks. He has been to the vet twice. First we thought it was because he had gotten into rotten food. The vet put him on Metronidazole and I added a powder suppliment to his food. The explosive diarrhea stopped and it looked like he would be better. Then his stools starting getting soft again. I brought him back and had a sample tested which came back clean. I with held food for 24hours gave him plenty of water then started him on chicken and rice diet. He accually had a semi hard poop. I started to put his regular food (Purina One for Large Dogs) back in slowly then the diarrhea came back. Thinking it was the food I put him back on chicken and rice. Stools got a little firmer so I started to slowly add Blue Bufflo basics with salmon and potato. It has been three days since the new food and in the mornings he has had diarrhea. (light brown not alot of smell ). I started to investigate where he spends his day when on his run and I notice the pine tree behind the deck is missing the entire bottom branches. Now I am not sure it is the food or that it is the pine tree.