I have often done the scale mash in a saucepan thing when planning a novel grain bill or water profile. Now I find Bru'n Water an excellent substitute to get me in the ballpark. In my experience, trying to adjust the pH during mashing is futile. Almost as soon as grain hits water, the buffer systems are set up and the mash pH will keep pulling toward its natural set point. You can shift it a bit, but it will move back. Plan ahead, and then check your actual pH. If it's off, just take notes, and adjust your water treatment accordingly next time. You may not be in the ideal range, but don't panic unless it's extreme -- below 5.0 or above 5.8. And note, pH is to be measured at room temperature, not 100°F. Alleged "correction factors" are wishful thinking, and higher temperatures will drastically shorten the life of your probe.