I've recently changed my thinking on water for dark beers. I knew that Kai's experiments have shown that roasted malts don't contribute as much acidity per SRM as crystal malts, and I've also lowered my target mash pH to 5.4-5.5 (@20C) as alkalinity/high pH are a major culprit in lifeless beer, extracting tannis and astringency, and other bad things. But AJ DeLange's posts (for example, here
) made me consider the possibility that I don't need any chalk in my water despite it's relatively low alkalinity.
I recently made a 40 SRM oatmeal stout with 2.5 pounds of roasted barley in the mash for a 12 gallon batch. Despite an alkalinity of only 48 (and RA of 25) in my tap water, I added no chalk or other carbonates. My mash pH was 5.5, and I wouldn't want it any higher.
One side note is that ColorPhast pH strips were almost unreadable in the dark wort, but looked like they read much lower than the meter. If I had to guess, the strips read around 4.8. With the error, that's still 5.1. The meter was just calibrated. I'm starting to question whether the ColorPhast strips are really worth using.