At the start of blooming phase, the plant will be consuming lots of Nitrogen from the lower solar leaves. From the images it looks to be just that. To counter this you could add nutrient additives fitting the soil you are using.
Hey, is it normal to be in the flowering phase? Because that's when the plant absorbs all the nitrogen reserves. And when it's in flowering, what the plant cares about eating more is PK... cheers, king! Good luck!