
Mate', I think this is a more uncommon symptom of K deficiency,... other, lower leaves look more typical, with the burned margin tips... The foliar spray isn't a part of this,... organics are generally mild nutes (you have GO Box nute's?), and as such can come up short in demand during bloom,.. She looks healthy otherwise, and pH needs to be really far off (acidic) to lockout, so most likely she's just having a lack-of defc.,... up the bloom dosage, or apply a stronger bloom booster (high P K) and see is this stops progression of symptoms.... Seems odd that the others are fine, but early mild K defc. doesn't show symptoms right away, plus, each pot becomes it's own little ecosystem, so even with the same feeds/schedule, things can still drift into trouble as individuals,... I'd start some Ca-mg anyway, as demand for those is increased as well at this stage-- prevention!