[EDIT: This post has been updated considering further information!]
I thought I'd dig a bit deeper to see if I could uncover something (it's all related to a project I'm on, so I don't mind).
Into my copy of Bru'n Water goes the water detail and grain bill for the recent brew of this thread (post #18).
My own water spreadsheet calculates alkalinity (shown in this thread "as HCO3"). Because it's calculated the water has to balance, and to get the HCO3 about 3, it needed a bit of padding out. There's always nitrate (often agricultural pollution) so I used that. 25mg/L, which is a bit high and a bit out of character with rest of the report but not at all unusual from an area of fairly modest intensity of agriculture (half the legal defined limit - 50mg/L -in the UK). The results are plugged into Bru'n Water:
"My spreadsheet" by-the-way is the, widely despised (I don't know why so many dislike it so much!), "Defuddler" linked in my forum signature below (blimey, I should charge for it!). It balances perfectly ... because it has to! (the "0.00" is what you're looking for).
The grain bill is plugged in, and the water details into the water adjustment page, and:
Ignore the red boxes, Martin is a little "draconian" with his "warnings"!
But the interesting box in that illustration is the "Estimated Mash pH". People in this thread do say ignore the attempts at predicting pH ... and it's true, it is virtually impossible to align the pH with a lot of physical measurements and
NO actual data concerning the very changeable acidity of the grains involved (the product of "natural forces" which folk do attempt to provide a value for - e.g. the very empirical "pH-DI" shenanigans). But as long as you know it's only "roughly", it's worth having a stab at it.
"Expected Mash pH" is 5.64. I think that's pretty close to
@Hartwa's conclusion?