m0useanswered grow question 10 months ago Maybe Calcium, but the leaves going crispy and stating green is reminiscent of root issues, is your medium draining well? is your PH on point in runoff?
I'd check these few things first and adjust if they are off. Also calibrate your tools if you have not in a while.
I myself do not like 20/4 lighting schedule and feel plants need a bit more down time. 18/6 is my ideal.
Best Of Luck!