Kaya666answered grow question 7 years ago High there! :) It's normal for leaves to go pale/yellow in LATE flower (i.e. last 2 weeks before harvest), but if your plants are not there yet, it's likely a nitrogen deficiency. Don't be afraid to supplement nitrogen in flower as long as you give some P & K along with it. A basic, cheap NPK fertilizer should do the trick. I had rapid chlorosis (yellowing) in Week 7 & was able to reverse it by applying a fertilizer called Tomato-Tone, which contains a 4-7-10 ratio of NPK. In the future, you can prevent this problem by continuing to feed a vegetative fertilizer all the way through the preflowering phase to ensure she has enough nitrogen to last until harvest.