X'-- No worries dude, that's mostly, if not entirely
normal fan leaf consumption for this stage of bloom,... the plant will remove what mobile nutes it needs from them to help fuel bud development,...mostly looks like N being stripped, but Mg defc. can also look a lot like N defc. in the early stages sometimes,... more typically, leaves
and veins going all yellow more or less evenly is typical N defc. sign,... this is certainly not Zn, or S defc.-- both are immobile nutes, and symptoms start on new growth first, and S defc. tends to soon affect the entire plant with pale off-color... And it can indeed happen fast at times! But, fact is, you want your girls finishing face first, looking a bit haggard, because it means the plant has really tapped into inner reserves of nutes, using and losing the extras, which makes for smoother tastier smoke,.. excess nute's remaining fouls the bud!
So, it's just normal support for the last stages of bud ripening,... your bloom nutes should have a little N in them, and some Ca-Mg now will be good too,... There's zero need to flush! In fact it'll likely make matters worse, stripping what little is in there, and forcing the plant to dig even deeper into it's reserves... ditto for stripping the affected leaves off, let the plant do that naturally when it's done with them. I don't see any other signs of trouble, but a pH reading is always a wise thing to check on... the AN nute's can buffer themselves in solution, but they don't control the soil/medium pH entirely! proper pH'ed input helps greatly, so it can seem like it's doing all the work, but it's not,.. too many other sources of pH influence in there!
...
you have a couple nice plants here mate-
... just keep me informed if the rate of yellowing stays fast, and other symptoms start showing, then it might be a pH issue....