I'm brewing with country rain water, which I'm assuming has little mineral content. And it's pH? As manticle said - largely irrelevant. My last brew day (to end up with 23 litres wort) had 6.6kg grain, the darkest being 120g Crystal 40L. Overall colour was 14 EBC, so a bit darker than a typical lager I'm supposing.
Point of this info? I take a sample of wort from the mash tun early in the mash, cool it, and measure pH (Hanna 98128 instrument). My target pH, at ambient temperature (nominally 25C) is 5.4 to 5.8 and that mash came in at 5.60 without adding any acid or acidulated malt. Salts added to this IPA were 7g Calcium Sulphate (Gypsum) and 4g Calcium Carbonate (chalk). Normally, using the KISS principle, I just add 4g CaCl and 4g Calcium Sulphate to my rainwater for a standard brew.
If I'm making a darker brew (porter, stout etc) I find I have to add 2 to 3g Calcium Hydroxide (pickling lime) to raise the pH up to where I need it. I do have lactic acid in my inventory, but have never had to use it.
As a point of interest, when I used to measure pH at mash temp, the ideal target was 5.1 to 5.5 however that practice (measuring at mash temps) is severely detrimental to the longevity of the sensor I have since learned. That info direct from Hanna! While the 98128 is rated at up to 60C, the advice I got last week was to keep it below 30C and double the life of the ($116) sensor.
