HELP! Rapid Change, Dry, Up-Curled Leaves at upper part only!

[MP07070]

Soil, 5gal fabric pots
Strain: John Herer
Lights: LED 12/12
Environment: 2x4 tent, fan, etc. Averaging 70F and 40-55%RH
Water: clear, spring. Every other day. Have been flushing for a few days, although this started prior to flush.
Fertilizer: LOTUS, was into the 4th week Flowering stage
pH in the 6.5-7 range. When it hit 8 I watered with a light white vinegar mix. No change in the leaves initially.

Upper Leaves started turning yellow with brown spots (see pics), Not dry (prior to trying to adjust pH!)
After a week (virtually overnight) the leaves turned up, went dry, they crumble if I squeeze the curled part of the leaf.
Been watering with straight spring water hoping for a reversal, or to at least maintain until the buds are ready to harvest.

Pictures and a link to pics.

https://imgur.com/a/aJsGcJK

[Rwise]

Ph issues, tighten up the range to 6.5 - 6.8, she is eating herself for the nutes she cant uptake.
See the link "Plant Problems" at the top of this page and match the photos.

[Fjeff]

Have a look, then correct the PH.

[MP07070]

THANKS! What is the best way to raise/lower pH? I have Cal/Mag and white vinegar on hand?

[woovygroovy]

General Hydroponics pH up/pH down. The kit comes with the tester solution and vial also.

[Rwise]

Vinegar is not stable, do this test, PH your water with vinegar then let it rest 24 hours and test the PH again.
I use pelleted lime and pelleted sulfur to buffer the soil.
Many things affect PH, for PH up I use liquid potash (labeled as PH up at the grow supply), for down sulfuric acid (careful that shit will burn you)
BTW I grow in soil.