well, you got a ton of leaves so a few dying is no big deal, but hints at an underlying issue - nutes, pH, ec etc...
Looks to be a mobile nutrient, since it's cannibalizing itself from bottom-up instead of where the most light is hitting. yellowing from tip -in.. and curling at bottom/older leaves.
Looks liek N-def... don't see any spots beside the one in pic 2 and could just be a blemish ro something else.
this could be normal.. could stick to your current schedule and see if plant is just shedding a few leaves, but i think it just needs a bit more N... or rais pH slightly if you think the concentrations and ratios of what you feed are proper already. raising pH a bit will help with availablility of N in the plant.