Is this a magnesium deficiency?

Well, one of my lower leaves have turned yellow in the corner (Just a little spot not even quite the size of my pinky nail) and then on one of the upper leaves there's a spot about the size of the tip of a dull pencil. They turned yellow, the brown, then crisp. I have Epsom Slat, should I add a little? If, that is, that its a mag deficiency?

/www.rollitup.org/marijuana-plant-problems/deficency-nute-burn-diagnostic ^
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Post a pic and look here^