Be careful to not overfeed either. I've found that the recommendations on the bag of Orijen are really the upper limit. We've found that cutting back slightly on the amount has helped to firm up puppies' stools.
Considering the age of your puppy, and the description of his stools, I'm also thinking more along the lines of intestinal parasites. When and how often has he been de-wormed and using which vet prescribed product?
"Education is a progressive discovery of our own ignorance." -Will Durant