I recently started using RO water produced from this thing:
The TDS meter (cheap amazon thing) reads 0 ppm. I used Bru'n Water to create a water profile for a Kolsch 15 lb pils, 8oz flaked wheat, 3 oz Acid Malt. Added 2.5 grams Calcium Chloride to mash water of 5.7 gallons. Bru'n water had my PH target at 5.41, but actual PH was closer to 5.1, and I had to tweak the mash with some pickling lime to reach 5.3. Ph meter is a milwaukee ph 53 and I calibrated to 4.01 solution, also chilled mash sample to room temperature.
Is this low PH common using RO water? I know there are lot's of variables here (malt, strength of acid malt etc...) but am I missing something big or is this sort of thing common? Am I just going to have to keep good notes and work it out? Any pointers or a sanity check of yea..well that's what you have to do would be helpful.