hmmm well pics would help, obviously. What I can recommend is do a flush on all your plants, just in case there is some buildup of ferts in your soil that is messing the plants up. After you flush, give them some fish emulsion right away, it's high in nitrogen and the plants love it (it's organic). I can't tell you specifically what's wrong without pics, but here is a great guide with pics of every problem, so check it out!

International Cannagraphic Magazine Forums - The Complete guide to Sick Plants,pH, and Pest troubles!