Anyone else had problems with Fromm?

[Erica]

So I dogsit for a mastiff (Zeus) extensively - I see him at least an hour every weekday, and often longer and on the weekends - and he's had soft stools since forever. Apparently, when he was a puppy, he had some sort of virus that gave him diarrhea, in addition to being on a pretty low-quality food (don't remember specifically, but it was Eukanuba or Purina or one of those big brand names). The vets switched him to Science Diet I/D, and that helped get him back on track, but after at least a year he still is eating with some I/D or gets really loose stools. Amadeus, the malamute he lives with, caught the virus and had diarrhea as well, but after the I/D got him healthy he was able to make the full switch to normal food. Right now they're on Fromm Large Breed Adult food (Zeus has about 3 cups Fromm and 1 cup ID for breakfast and dinner), but I've found some reviews saying that other dogs have had loose stools on Fromm. Can anyone verify that? I've told his owners and they're going to talk to the vet about it. There's a wonderful store in our town that has lots of different natural dog foods...if Fromm is the problem, can anyone recommend what brands of food to look for and which to avoid?