i have said it twice and seeing as i'm posting again i might as well re iterate.
the plant is hungry!, that is why it looks like shit.
there is food stored in the soil, when the plant becomes too big for the pot it will require either transplanting to an appropriate container size or feeding with the bottled nutes you have. the soil is depleted so you need to supplement with the VEG solution at MAXIMUM directed strength. feeding with a complete and balanced plant food will ensure the best health as opposed to trying to rectify a problem by adding one or two elements.
if you are currently feeding full strength veg nutes every watering and you continue to see the problem worsen then discount my information but i am confident as can be that if you do that the problem will stop. and no those leaves will never ever be deep dark healthy green so try to concentrate on the new growth up top.