I recall Martin saying the difference had to do with something about the different data sets the spreadsheets used to estimate the pH impact from the various malts. Like Denny I find Bru’n Water to better match what I’m actually measuring for pH in the mash. I measured the pH of a bunch of mashes as I was getting comfortable building water and understanding mash pH but Bru’n Water has been so consistently accurate I often get lazy and won’t even measure the pH any more, particularly if it is similar to a beer that I’ve brewed before.
