So close to finishing flowering... Please help diagnose with picture! Excellent info.

I have a Jack Herer, about 5-6 weeks into flower. Using Cal-Mag Botanicare Flower Bloom, Liquid Karma. It's about 5 and a half feet in a five gallon Pot.

Humidity is about 35-50 consistently and heat is 68-80 from night to day.
Flushed two days ago and then added Cal-Mag next day because almost positive I had a magnesium problem and didn't want to flush all of it out.

PPM of runoff was 900 and PH is 6.8. Here is my picture of one leaf that accurately describes what is happening but the other leaves are almost completely yellow and slightly drooping.

lower leaves, right? at this stage of flowering, I wouldn't worry about that, N def. You can provide some more N if you want but I don't find it necessary, as long as the upper leaves stay ok.