Brown Spots & Dying Leaves - Org Nutes not helping & PH looks ok but maybe not - wPic

Hi, I am new here and new to growing. This will be my second time writing this as everything just deleted when I accidentally navigated away

I am having a serious problem with my one and only plant and first real attempt at growing. I'll be starting back from seed if someone can't help me figure this out quick! I hope to pass it forward when I get the hang of things. I've done a fair amount of reading but don't think there is time to screw around guessing anymore.

Plant Specs:
1.5 months old
11-12 inches (stunted growth?)
Grape Ape from bagseed (Whatever that means as I read it is technically a clone only strain?)

Lighting: 4x23 watt CFL 5000K 1600bulb/6400total lumens
Lighting Schedule: 18/6
Temp: 75-90F in a room with AC but I try to keep it stable
Soil: Self mix of 10% vermiculite 45/45 peat moss and garden store composts (I thought I could get by without added nutrients)
PH: Looks like 6.5 but hard to tell, I have a kit that uses color changing powder to mix with soil and water (maybe I need a better tester?)
Feeding: Just started Earth Juice Grow, and have been using filtered tap (I will switch to distilled) Watering every 3-5 days, sometimes when still slightly moist 2 inches or so down.
Humidity: Not sure, maybe too dry due to the AC in the room. Misting 1-3 times a day and have kept a pan of water in the box with it.
Grow Area: Custom box with pc fans for vent in and out - I usually leave the door open

It's clear it's in rough shape from the picture but the problem is dying leaves with spreading brown spots. It started out a few weeks ago with the bottom most leaves slowly turning yellow and drying out. I finally cut their shriveled masses off the other day but the problem is speeding up and spreading. Adding the organic nutrients 4 days ago does not seem to have helped and if anything it has gotten worse since then. Some of the biggest leaves are gone and the new ones down lower aren't growing. The growth is basically at a standstill and I think it has been abnormally slow throughout. I think something has been wrong for awhile and my best guesses are the PH despite my seemingly successful attempt to test it and the fact that I may have been over-watering although it usually seems quite dry in between waterings.

Thanks for any help! Together maybe we can save a life

*If the pic goes down I'll try to repost it in a response.

I think your PH is too high and locked out phosphorus, cal, and or mag. Necrosis on older leaves usually means it a mobile nute being locked out.

Ok thanks that is very helpful. So I'll track down some sulfur or just head to the grow store and see what they recommend to lower ph.

I decided to re-pot in a larger container of purchased soil rather than try to mess with the PH of what I had. It is recovering and looking much better.

5.5-6.5 is perfect p.h. If it is nuetrient lock out you need to flush with distilled water or r.o. water or water with a leaching solution like final flush added, DO NOT add sulfer because if you are dealing with nuetrient lock out it is built up sulfer and nitrogen on the roots that you are trying to flush (magnesium sulfate is better in flower than magnesium nitrate because it promotes developement of essential oils like T.H.C. despite the weekly flushing required to avoid lock out) But I would flush with 2 times the amount of water as soil ( 5 gal pot flush with 10 gallons of distilled or r.o water and on the final gallon add a light nuetrient solution make sure to add a small dose of Cal mag 3.5ml or so per gallon so and a well rounded base nuetrients N/P/K, it will be two days or so before you need to water again make sure not to over water regularly to avoid root rot.If using a leaching solution u only need to use as directed on label and enough so some comes out the bottom, the next day water with nuetrient solution described above. hope this helps your plant!