I’m surprised that your vet recommended a grain free food as there is currently an investigation going on possibly linking grain free boutique foods to Dilated Cardiomyopathy.
I would do another fecal test. Giardia is common in puppies and can be intermittent. Have you tried adding a probiotic to his food? Sometimes after taking antibiotics, their tummy can get out of whack. I would try adding FortiFlora and maybe a little fiber to the diet to see if that works.
I’ve switched my dogs foods several times over the years. But, I finally saw the light and now feed either Purina ProPlan or Purina One and their “output” is consistently good.
Best of luck to you.
