This. ....... sounds exactly like what happened to my girl. Went a bit too hard on pk 13 14 at week 3 flower to week 4. Fan leaves have mostly all yellowed and died because of it.OK then,,,what flowering P&K supplement are you giving them, hmm?
I'll bet dimes to dollars your applying to much P&K WAY to early. P&K tox. They won't come back to green so just cut the P&K supplementation and run your BASE flower nutrients!
Bearded - your close. P&K total is what for your feed solution?
Bloom boosters can be snake oil to those who do not properly apply them......Keep in mind that the manufacturers want you to use it and by more......so overuse for many reasons tends to be the #1 problem I see around here!
Next time I'm going to be a lot more careful adding that shit.