I agree plants look hungry. Its not normal to have that many yellow leaves at this stage. Plants should be green, and growing like hell. At this stage they should most likely be using the most fertilizer than theyve ever used in their lives.
Many also still believe in cutting back Nitrogen during flowering, when all thats needed is correct ratio. Right before, and mid bloom, is when plants will, or should use the most food, and water, as during this time, they will put on more mass, than they ever did during veg. Not counting producing more/different hormones, terpenes, ect.
All nitrogen is, is Protein. When humans eat chicken, fish, eggs ect, our bodies turn the protein of the flesh, into nitrogen/amino acids. Plants skip this process, unless you do like the Native Americans did and put a fish in your corn hole.
The big reason why Bodybuilders eat protein every 2-4 hours, and keep their bodies in Positive Nitrogen Retention, or your body will start catabolizing itself, for energy, just like the plant does. The leaves turn yellow, and eventually go necrotic.
Protein, means of first importance. Protein is responsible for every metabolic function, including cell mitosis/division., immune response. Supports creation of hormones, and all other chemicals.
Taking protein from a plant during flowering is like taking protein from a bodybuilder, or strength athlete, though marathoners have a great need for protein. Magnesium, Sulfur, and Calcium, are also extremely important.