While that sounds like a healthy food, it has so many ingrediants it would be hard to find the culprit. Healthy foods cause allergies as well. There are dog foods with only three or four ingrediants, or you could home cook for a week and see if that clears it up. At least you would know what goes into it. Here's a site that gives a sample diet, for a short time a week or so, you wouldn't need to worry about adding the suppliment.
http://support.mspca.org/site/DocSer...pdf?docID=1562 If the tearing clears up 50%, the first week, I'd say food is the problem, you might not get 100% clear up for a few months.