overfeeding K is a valid conclusion with some interveinal chlorosis down there (caught fast it seems), but i vote for (if PH in soil is OK and temps don't vary too much) still too little - just a little. They degrade slowly and the yellow but full intact fans tell about some N lack, the degrading fans tell a P def (can't see very well, new growth tips are slight yellow and go look like burnt like N?). So perhaps those interveinal clorosis symptoms may come from a real lack Mg and overall....
Concluding that you did well until now and you appear to have been more conservative with nutes:
Perhaps step back with bb a little and go up with overall strength.
But don't go microcontrolling - looking not too bad for a nice harvest in 3 Weeks. I guess they will not really need stronger feed the last weeks, you might just be at the climax the days around.
EC meter? get one for next run.
Cheers, still looking nice!