I recently moved to Rhode Island and my mash efficiency has suffered. The main part of my process that has changed is the water. The pH as measured by colorpHast strips (and two other off brands) starts out around 5.5 (with the systematic error of 0.3 as observed by Braukaiser, that's 5.8).
This pH is ridiculously low to work with, and I've been having a hard time. I've used more calcium carbonate (chalk) and sodium bicarbonate (baking soda) than I like to raise the pH to acceptable levels in the mash (it gets to the 4-5 pH range even with a mash of around 14 SRM).
I've also taken to steeping roasted (and really any 100+ Lovibond grain) grains for pretty much every beer I mash to avoid dropping the pH with darker grains.
What else can I use to raise the pH?
I've heard sodium hydroxide (food grade) might be usable, but I have no experience with it and haven't found much about it with regard to mashing wort. It's also caustic and somewhat dangerous to handle from what I hear.
I've also heard that calcium hydroxide (used for pickling) is an option. I think I might order some of this from Amazon and try it out.