Leafs dying, Pls help

Looks like Calcium deficiency. While Flowering always use 5ml per gal of Cal-Mag Plus with your nutrient solution.

Your bush doesnt need those leaves anymore. The yellowing is normal in late flowering, but the plant is basically stealing nutrients from those leaves. Obviously, those leaves are under the canopy (dont get light) and your plant is telling you that it doesnt need them. You are ok for sure. Canopy pic looks excellent.

Have a look at both posts, especially what cause it https://www.growweedeasy.com/cannabis-plant-problems/potassium-deficiency https://organitek.com/potassium-deficiency-in-cannabis-plants/#:~:text=Yellowing%20or%20browning%20of%20leaf,the%20leaves%2C%20if%20not%20addressed.

Perfectly normal as they go into flower to start cannibalizing those lower leaves. Just defoliate them and business as usual.