Yellow leaves

if you have feed a lot, it's possibly a p tox? or if you haven't fed much, it could be a k-def... hard to say for certain. is it isolated to the bottom leaves? while it could be a sign that you need to adjust your feed slightly, that's less of a problem. Plants will shed lower leaves, but if feed well they also will not shed their lower leaves -- except for maybe late in bloom even in that context some just get dropped.

From the color of the leaves, it would seem a lack of nitrogen and potassium, have you checked the output pH? If it is out of the norm, flush at the correct pH, then feed your plant with 1/2 - 3/4 of the dose of nutrients. I would also add a 0.5 ml / l of cal / mag for 1 week.

It's normal for some bottom leaves to yellow and die after starting to flower. If you see it start to creep up to other leaves that's when you should worry. To me looks like she's self pruning! Happy growing !