I see signs of a pest eating on that leaf but not sure about the discoloration. Possibly some liquid got on it during lights on? I see it on another leaf or 2.
Picture of the whole plant see some yellowing on the plant behind your hand
Hmmm are there any brown spots on the leaves? Was this plant ever outside
Nothing I’d worry about just a normal amount of nitrogen and phosphorus deficiency you’d get that late into flower
Pretty purple, what is it?
It’s typical for a plant to shed lower leaves as the plant matures.