I'm WAY too stupid to help you but page 125 of Indoor Marijuana Horticulture by Jorge Cervantes (GET THIS BOOK!!!!!! ) has a picture of the same problem and states that it is a potassium (K) deficiency.Basicly he says to fertilize w/ a complete N-P-K and add a organtic potash and water mixture, with a pre-application PH of 6.5. Foliar feedind in this situation is not recommened. I spent over $100.00 on five different books before a friend let me borrow the only one (M.H.I.) I needed to buy. What the fu............. He has listed his website on the book as www.marijuanagrowing.com . I have yet to look this over (I can't put down the book!!) but if it's anything like the book then it will be time well spent,trust me..... Also, I was wondering if your containers have any drainage and/or holes? It seems like your leaves are curling (down) in a way that they do when they are over watered..........do you have a mixed soil or any additives to inprove drainage? Maybe you should....... Roots love the big O (as in Oxygen)-That's NOT from the book but it's never really bad advice, you know......