Does it look like growth is slowing or stopping too much (even though you're in the flowering stage), twisting of new growth, yellowing beginning at the edge of new leaf growth and then over the entire leaf ? If so, you could have a magnesium deficiency. This is what my grow book has to say about it, "The Best of Ask Ed: Your Marijuana Questions Answered": Quote: At the first sign of deficiency, Epsom salts should be used. The magnesium-deficient plants were sprayed to dripping once with a solution of 1 teaspoon per gallon of Epsom Salts (MgSO4), which was also added to the water in the rate of 1 teaspoon per gallon. The new growth exhibited no signs of deficiency. :Unquote