Help Please - First grow - Week 7 flowering - Yellowing and dying

[SRG CPT Weed]

Hello,week 7 and 2 days from switch to 12/12,they been yellowing more and more in days,some say its normal,others look for problems and give some N,so what you guys think? Lower new growth seems to suffer from N def,and I was hoping to harvest little buds sometime but low low new undergrowth just kind a turning to salad and dying,before was feeded good with N like 20-40-40,couple weeks started 12-40-12,have few 1500ppm waterings in a row,maybe too much P locked up N? PH seems in range between 6-7.If hairs were brown I wouldnt worry but they seem to be left white so I guess I still have 4 weeks to flower,what ideas?
400 + 600w hps.

 

[NuttyProfessor]

its pretty normal they dont use N in flower more p and k your buds look great , i could be wrong but with most of mine all the leaves almost die off

if in doubt flush the hell out of them and start of slowly again with nutes

 

[NuttyProfessor]

just looked more closely to pictures there is something not normal , id flush like mad , get a good ph and start nutes again slowly ,

 

[SRG CPT Weed]

just looked more closely to pictures there is something not normal , id flush like mad , get a good ph and start nutes again slowly ,

Thanks a bunch for reply! I was watering today and I checked PH of bigger pots and it was like 5 :*( I was always checking smaller pots and I just not remembered the pot I was checking most usually had even raised ph before,so it was highest ph from all..It was like that for a week or two maybe,lets hope damage is not too big.

 

[SRG CPT Weed]

Any more reviews? Is it normal? Because my hairs are still WHITE...tomorrow will be exact 2 months time from flip,ofcourse those pics are like week behind but anyway,not much of a difference,im worrying about growth for month more with dead leaves lol...