before any nutrient treatment, check the roots. your plant might be root-bound and/or your roots might be sick or infected with bugs. foliar spraying of a light nute mix will work faster than through the roots and you will be able to see improvements (or not) in a day or two. just do not do any heavy feeding of any type. it's kind-of-late now, but i would of re-potted the plant (up to 2 weeks into flower) into a bigger container.
IMO... systemic yellowing and dying of bottom leaves is an indication of root issues. the NPK ratios of most bloom nutrients should be able to sustain a plant throughout its life cycle.
