Are you using any nutrients? Mine will tend to look like that when i over fertilize. IMO I would only cut leaves off if absolutely necessary. They will fall off or pull off real easy when they are ready. I wouldnt think it was nitrogen deficiency because they are still pretty green. ND usually causes multiple leaves to yellow. Im still a noob so maybe someone with more experience will pipe in. Just out of curiosity, why are you on that light schedule? How come you dont run 18/6, 20/4, 24 etc?