Hi T S-
Bringing him to the vet for a skin scrape to determine that the issue is in fact yeast is a good place to start.
His yeast also may have nothing to do with food allergies at all, which is why the change in food has not helped.
You may also want to talk with his breeder to see if the parents had any of these issues or any of his littermates.
My pitbull has both food allergies (diganosed by elimination trial) and suspected environmental allergies. During the summer months I bathe him twice a week in Malaseb shampoo, which contains 2% chlorhexidine and 2% miconazole. Chlorhexidine is a gentle, but effective antiseptic and miconazole is the active ingredient that will kill excess yeast on the skin. I would highly recommend that shampoo over your current bathing regime. It makes him very soft and no dander at all.
