Plants 2 weeks into flower...Looking for advice on whats wrong..Pics inside! Help!

Alright so my babys are 2 weeks into flowering. The strain is kings kush. Temps are good and humitidy is also good. Im growing in pro mix hp and using dry mix in nutrients in the bloom phase. The npk for the nutrients is 12-34-12. Upper half of the plants look great and healthy! Bottom half are starting to show signs on the pics posted. Adjusting ph to 6.5 for feeding and flushing with just straight water..no ph adjustment. Ive put a bit of lime in the soil as a buffer thinking maybe the pro mix has gone acidic which iv heard can happen sometimes. Also there is a fan on the floor constatntly blowing air at the bottom of the plants. Could this constant air be drying out those leaves? Ive tried reading up on what i can but i cant seem to find an accurate diganosis. Any advice or help would be much appreciated. Take a look at the pics and tell me what you think. Cheers!

The pots need to be 2x that size to avoid this, once its been rootbound too long it starts yellowing/browning and dropping leaves. Also those nutes are no good ,too much P locks out N and other trace/micro elements, get some hydro nutes and use every watering.

why no ph adjustment on your water?

this could be ph fluctuation.