Your pH swings arent helping. The pH meter will definitely help going forward. Magnesium yes but all the other usual suspects too.
Actually its not using ATP to move nutrients or sugars. Thats all done on a concentration gradient or osmosis.
Those old ugly leaves aint doing shit. And yes the flower is doing majority of photosynthesis for itself. The fan leaves contribute little carbon to the flowers themselves.
As far along as you are in flower feeding is more effective than letting the plant "eat itself".
You could do nothing and it would be fine. But as a practice of good plant hygiene you would clip them.