What did the vet say about his hocks and pasterns? I do think we're too quick to jump on the no grains bandwagon sometimes. It wasn't that long ago that most people fed their dogs mainly grains (oat, barley, rice) with some offal mixed in or whatever the animal hunted, but the huge bulk of their diet was grains and dogs did just fine on that. I mean, arguably part of what makes a domestic dog a dog is their ability to digest starch with far more copies of the gene that produces amylase than any other canid. There are absolutely dogs out there who don't tolerate specific grains well, but the vast majority of dogs do fine with grains and when you hear hooves, think horses, not zebras. This is a puppy, puppies are notorious for finicky tummies and occasional loose stools. If he was having normal weight gain and normal output before on this diet, I wouldn't rush to change the diet without examining other causes too. Particularly since he *was* diagnosed with giardia which is notoriously hard to clear. Zero point in going grain-free if the issue is parasites. Deal with the parasites first, make sure they've cleared, and at that point, if the runny output continues, explore food options.