Maybe k-burn.. that typically is a high ppm in feed. if those leaves are skinnier than normal (can't tell, looks sativa too), that's another indicator.
your top leaves would have interveinal chlorosis, so that kinda eliminates that...
Think it could be Sulfur toxicity? if that makes sense relative to recent feeding.
it's looks really healthy otherwise, so don't be afraid of wait-and-see option. extra water-only irrigations in bloom only set you back a bit, even when neccessary.