What is this problem? - Pics

I have 4 white widow plants under a 600w hps. I'm 3 days into flowering, but the plants have been showing these symptoms for a few weeks. I've been feeding 2/3 strength Fox Farm grow big (2 tsp per gallon), 1 tsp cal mag and one tbsp big bloom in RO water every other watering. I'm only watering every 5-7 days, so feeding every 10-14 days, is that long enough to cause a deficiency? PH of water and nutes has been 6.6-6.8. I was really hoping this would kind of self correct since as far as I can tell I am doing everything correct, but it seems to be staying the same or getting worse. The clipping in the picture is from near the top of the plant. I fed them on the last watering, so I really dont know what to do at this point. They are about ready for another watering, should I flush them? Feed them? Just water as usual (which would be 5-10% run off)?

Looks like some N Def. also are you growin in soil? if so PH should be 6.0 - 6.5 no more or some nuts will get locked out.

Roll&Grow said:

Looks like some N Def. also are you growin in soil? if so PH should be 6.0 - 6.5 no more or some nuts will get locked out.

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If this is the case PH could definitely be my problem then. I've been following the Jorge Cervantes Medical Growers Bible and it says 6.5-7 for soil. Is this generally considered to high? I've been trying to get my water/nutrients to 6.7-6.8, but I might have been closer to 6.9-7 on the last couple waterings before I got the hang of my ph meter. Should I try watering with ph 6.5 water and just give it some time?

They were fed on the last watering with 2 tsp/gal of Grow Big (6-4-4) so I think there is probably sufficient N in the soil, but possible I am undergoing the nutes. I've always been told that is is way easier to over do the chemical ferts than under so I've been feeding 1/3-2/3 strength, is it possible that just isn't enough?

After doing some searching it looks like most ppl recommend 6.6-6.8 for soil but others say 5.8-6.4. Which is correct? Why the difference?

Any advice? I think Im going to flush with 6.5 ph water unless anyone thinks I should feed instead.

Well i had the same problem i was feeding my plant with 5.7 PH nut solution but i started to see some def. i flushed them , let them dry for 1 day and then feed them with a 6.5 PH nuts, in less than 12H you could see the change.

They need N as in Nitrogen.

Yea dude. I would increase that feeding schedule. 5-7 days between watering is a lot, but 10-14 for feeding (nutes) is way to long imo. I feed nutes twice a week.. Usually on Sunday and Thursday.. Both feedings get nutes. Never just water. They are begging you for some N.