What you're seeing on your plant isn't exactly necrosis from hunger, but rather an issue with light efficiency and energy management.
You have an extremely dense canopy. The problem is that when the leaves overlap so much, the ones underneath stop producing energy and start consuming it just to stay alive; they become parasites of the plant. That energy and nutrient expenditure should be going to your new buds.
Here's what you need to do to get it in order:
Selective defoliation (Leaf pruning): Don't be afraid, in this case, it's more than necessary. Remove the larger leaves that are blocking light to the lower buds. You have so much green area that the plant won't even feel the lack of those leaves; on the contrary, you'll be taking a weight off its shoulders.
Direct light to the buds: As soon as the light hits those little branches that are currently in the shade, you'll notice they grow with much more vigor. The plant will stop wasting energy on maintaining overlapping leaves and will send it to the growth points.
Air circulation: With so many leaves together, the air doesn't flow, and the plant can't transpire well. By pruning, the air will flow better, and that speeds up the metabolism.
About your numbers (PPM): Having 400 in and 300 out ppm means the plant is indeed eating, but it's slow. As soon as you do the pruning and the light activates more points of the plant, you'll see it start to eat more because its metabolism will "wake up."
In summary: Yes, you can (and should) remove those leaves that aren't photosynthesizing optimally. You'll see that instead of stressing out, the plant will thank you by growing stronger.