PH or nutrient issue???

1.
This leaf is from a plant that is 5 weeks into flowering. Plants are around 5 ft tall. Ignore vegging plants in the background.

2. This is an indoor 600w tent grow.

3. These plants are grown in self watering buckets. I water them whenever the bottom reservoir is empty or 4 days after the reservoir is empty. In flower the water in the reservoir is usually gone 4 to 5 days.

4. I'm using Pro Mix HP in custom 5 gallon self watering buckets and using Thom's Custom Recipe minus the Drip Clean. Ph is usually in between 6.3-6.5.

5. This plant is 5 weeks into flowering. In flowering I go back and forth from feed, to plain water, to feed, etc.

Can plants really be affected with the Ph bouncing in between 6.3 to 6.5? Or could this be a nutrient burn? Thanks in advance!

thats nutrient burn.. Lay off the N, especially that late in flower..

LOL, I have some of this as well, guess I should follow my own advice..

do you spray your plants at all while the lights are on?

Yes I spray with Azamax with the lights on. But I doubt it's light burn because the rest of the plants don't have any issues.

It does look like light burn. Usually more pronounced when using Amax or neem oil.
Are they all the same strain?
Is the affected one in a more intense area of the garden?