Huh, well, I usually target a pH of 5.3 for every beer. Maybe I should change that. I was thinking about residual alkalinity the other day. If I use phosphoric to adjust my tap water to get the proper mash pH, the alkalinity and residual alkalinity goes waaaaaaay down. That's a problem, right? I'd only be adding a milliliter or less to the mash water.
Say, for an amber lager where I want to get the mash pH down to 5.4. With my tap water I need to add maybe .8 to 1mL of 85% phosphoric to get the pH down. But the RA drops to like -75, which is really low and off the charts in Bru'n water. This is why I usually use a couple ounces of acid malt instead, although that probably does the same thing to the RA.