I'm not quite as good as being a plant doctor anymore, but I'm starting to get concerned... is this a nutrient burn or deficiency? should I be adding food or flushing? WTF is the issue with these leaves? if seems to be spreading... http://i.imgur.com/oUxgu.jpg
the picture quality sux, but Im fairly sure thats some hardcore nute burn. just google "cannabis nuntrient burn" and compare the pics to what you see... thats a simple technique that i like to use... you can actually find lists of descriptions of deficiency and overdose signs, often with a picture each. some of the time theres gonna be more than one that kinda matches, then its a good idea to google the possibilities for pictures. odds are that youre gonna find something that looks exactly like your problem and somewhere on that page theres gonna be an explanation.
Actually I was looking through these http://forum.grasscity.com/sick-plants-problems/246040-deficency-nute-burn-pics.html earlier, and they look like mag deficiency more than anything to me.. yellowing then brown spots, drying out starting with the oldest leaves..