Rethinking the no N theory

So I started seeing yellow leaves on my Chocolate Haze plants at 6 weeks of true flower and dont like to see that until a week before harvest. I checked the sap and sure enough it was high PH and that is supposed to mean a lack of N.  I added some Jacks Part B at 1/4 strength, its 15% Nitrate Nitrogen and 18% calcium. We shall see.