My water is very low in sodium (7ppm), fairly hard (185ppm total CaCO3), and sorta low pH (7.7).
"5.2" has worked for me.
In a side-by-side comparison of using straight tap water v. tap water treated with 1 Tbsp "5.2" I had the results as followed (note these are pH at actual mash temp - yes, I know that's bad for the probe, but they were calibrated at that temp as well):
post mash pH w/o "5.2": 5.45
post mash pH w/ "5.2": 5.18
mid sparge pH w/o "5.2": 5.82
mid sparge pH w/ "5.2": 5.29
This is the first report I have ever seen by someone using a pH meter and who apparently knows how to use one to the effect that "5.2" 'works' so it is very interesting. We know that the product can't be buffering at 5.2 because it has so little buffering capacity so something else must be going on. Here's what I think it must be: Five gallons of water at pH 7.7 with alkalinity of 185 (to match the hardness i.e. assuming all the hardness is temporary) to which 5 grams (about a tsp full) of monobasic sodium phosphate (which is what "5.2" is mostly composed of) will settle at a pH of about 6.67. At that pH the water will be saturated WRT apatite with as little as 3 mg/L calcium (calcium hardness of 7.4 ppm as CaCO3). As the water in question doubtless contains a lot more calcium hardness than this it is clear that it will be super saturated (at pH 6.79) and I would expect that if you dissolved the "5.2" in small amount of RO or DI water and added that to the tap water a precipitate would form and the pH would drop as a consequence.
Now if the pH be lowered to 5.45 with some acid other than phosphoric this water, dosed with "5.2" as above, would not be saturated WRT apatite. But if it were acidified with phosphoric acid it would be close to saturation. So this is what I think is happening. The mash doesn't contain phosphoric acid but it does contain a lot of phosphate - enough that a pH drop can be expected when any amount of calcium ion is present. Here you have quite a bit of calcium and there is doubtless a shift of a couple of tenths pH because of that without "5.2". Augment the phosphate with "5.2" and saturation becomes super saturation, more calcium precipitates and there is an additional drop in pH (beyond Kolbach's observation) from the additional protons released.
I'm not saying that this is indeed the explanation but it seems to make sense and, in fact, has given me insight as to how "5.2" does what it is able to do which is, in most cases, lower pH a bit but not nearly as much as claimed. Perhaps the way to meet the label's claim is simply to add a ton of calcium to your mash or mash liquor.
Grain bill was 10lb 2-row, 1lb munich, 0.75lb 60L, and 0.5lb flaked barley
Mash was 1.268qt/lb
Now, with that being said, it seemed to work for me in this specific instance, probably due to the grain bill, water already low in sodium, and moderately low pH.
I've since gone to building water using my tap water and additions of CaCl, CaSO4, and lactic acid as needed for the profile I'm looking for.
I'm in the "don't use 5.2" camp, even though in some limited circumstances, it has, in fact worked as advertised for me. Mainly, I don't recommend using it because 1) it's been proven time and time again to
not work for lots and lots of people, and 2) building water is so dang easy with just a bit of playing around with Bru'N Water or the other calculators out there.[/QUOTE]