Some dogs simply get really soft stool on BB, so that may have something to do with it.
OP- I would also recommend Taste of the Wild, Solid Gold, Fromm, Kirkland, or Innova. All are very good foods with good ingredients. Out of these though, just make sure your pup does well on them.
Mom To~ Dakoda (b/t GSD), Acheron (black GSD)