czarstroke

It's normal for lower leaves to yellow and die off as a result of self pruning.. 👊

That looks like nitrogen deficiency to me.

Looks to be a nitrogen deficiency,Because nitrogen is one of the most common nutrients that you’ll find in marijuana, it’s also common for it to be deficient in some way. Nitrogen plays an important role in many of the plant’s functions including the production of amino acids and the vitality of photosynthesis. Any deficiencies of nitrogen in the marijuana plant will manifest themselves first in the yellowing of the leaves. The leaves will start to curl in and die if the deficiency isn’t treated fast. The deficiency works its way up from the bottom leaves to the top leaves.

Your canopy is strong. It does look like it's sucking N from lower leaves, but that's not 100% certain from this vantage point, either. (i don't want to encourage anything without due dilligence.) I see you have a multi part system of ferts. Try raising the one with most N proportion by 5% or 10% - some small incremental amount and see if it halts the issue and whether something new starts... i.e. may have to revert if the plant says so. knowing your ppm of N fed would help too.. if near 120ppm, it's probably fine on that front and something else may be the cause. With this knowledge you can avoid my first suggestion and the problems it would have possibly caused. pH, concentration and ratios of the nutes all will have a say in what is "right" amount and proportion for that particular plant. In some cases a formula will work well, but more optimally at a different pH and slightly different formula... it's really complicated stuff, actually. Small incremental changes, and wait for it to show the full reaction to what you are doing (unless it's a nosedive, of course). With notes and if neccessary, you can assess a different approach the next grow from beginning and possibly avoid all problems.