is it darker below, or did the darkness come in bottom-up? that would better identify a nitrogen toxicity.
contortion is likely something else, though.
first, ensure ph is right. Your plant is lush, so safest way is a water-only irrgation for a second or two. Getting any overabundance of nutrients in check may fix the problem on its own. if you were doing every-other irrigation, do every third etc... i'd dial back slowly since you are in bloom.