I PH my water to between 6.5-7.0 7.0 being neutral.
Subs mix which is self feeding calls for not phing maybe if you have heavy/chlorinated city water let it sit out for like 24 or so hours before use.
To be honest, I have my own soil mix similar to Sub's but not as hot, i used to supplement with light feed/nutes and I mean light watering like every 2ish days, with light water adding inbetween with great success.
Once my partner and his "professional grower" buddy starting nagging to ph the water we / I ( as head dude / only real sugar daddy for my girls ) have had more problems/nute issues etc. then I had ever had all my prior grows, some of my best looking btw I did poo, and didnt know much let alone to ph water.
Like was stated above a good neutral i.e. ph, will allow the plant and soil to find a happy meduim and develop its own symbiosis for the plant and soils success, once you go like lower then 6.8 higher then 7.3-7.4 ( most tap water is 6.8-7.2-7.4 in my expierance ) you have issues. Most R.O water I get is about 6.9-7.0 which most people would PH down :-/ ....... my tap water is 7.2 nearly always with 320-330 ppm, the well water at parents which is a ways away, and very nice and fresh well water is about 7.2-7.4 with about 500 ppm. O.K. my point being I have been more successful must using the water as it comes and not messing with the ph, the soil and pockets of alkaline material or acidic material will osomosize in and help the balance as well.
Also when i was using light-med so 1/4-1/2 strength organic bottled stuff, I still never phed and I think only had 1 issues once..... again now that I have been "phing" and such have had more issues this 1 start of grow then the 3 completed ones prior.
I think soi/ living soil and a good mix is much more balanced and flexible / forgiving then people think unless of course your tap / neutral water is like 5.5-6.0 or 7.5-8.0 on a consistant basis.