Leo is on a grain free & raw diet, with some carrots and no drinking water from the tap (we are on city water)..... I believe where he came from he was on well water and on the white half of his face, his tear stain was pretty prominant. I have not used anything on him, other than the water change, and every single morning, he gets a warm wash cloth (just wet, no soap or anything) to his face and folds, and over the past 4 months that we have had him, that tear stain has significantly disappeared!

Yah!
Here is his face when we first got him:
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And here is a more recent photo (Christmas):
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Ignore the last picture, I can't seem to delete it, but it's also a picture of when we first got him. (the thumbnail attachment)