Originally Posted by GilaMinumBeer
I was thinking the same thing, just change the concentration but notice playing around that the RA changes quite a bit with even small doses of HCl and wasn't sure about the Phos given it has, as I understand, more Hydrogen to exchange plus it is cited as effecting Calcium by Palmer.
At 75% concentration, it does free more H+ ions than 37% HCL. I've found the 42% conversion to be reliable, but my water has a lower temporary hardness than yours.
About calcium precipitation, yes some of the phosphates will bind with the calcium to form insoluble calcium phosphate in the mash. But, to put this in perspective, malt contains phosphates that do the exact same thing. I have yet to see a spreadsheet that accounts for calcium loss due to the presence of malt phosphates.
You also lose calcium in the mash to insoluble calcium proteinate (chelation from amino acids) and calcium oxalate (aka beer stone). I combat these losses of calcium by dosing the sparge water with equal amounts of calcium chloride (same as I add to the mash).
Bottom line - For the volume of phosphoric acid you're adding (2 - 5 ml per 10 gallons), the calcium loss is negligible. Like all things, moderation is best. Overdoing the brewing salts and/or acid additions is an easy way to mess up the water flavor profile.
For example, after experimenting with 5.2 Buffer and chatting with Kaiser, I've stopped using it all together. Once you nail down your water chemistry, at best it's unnecessary and at worst it adds a salty flavor to your beer.