Mash pH for Brew in a Bag, No-Sparge, and Decoction Mashing
Controlling your mash pH is a critical concern for all brewers using all-grain, but can be a special concern for those using Brew-in-a-bag (BIAB) or decoction mashes with high water to grain ratios. The larger water to grain ratios used in these mashes can lead to higher mash pH during conversion, so brewers need to take additional care working with these methods.
Mash pH for Brew in a Bag, No-Sparge, and Decoction Mashing
http://beersmith.com/blog/2015/06/05/mash-ph-for-brew-in-a-bag-no-sparge-and-decoction-mashing/