I'm no expert on water chemistry, but if I determine that I want to add something to adjust my water I add it to the mash water before doughing in. I will also add it to my sparge water. If I add acid to my mash water, I won't add it to the sparge water though. I did this once and ended up with a very bad beer from pulling tannins out of the husks. I probably added to much, but I'm like a wounded dog on this one. I won't make that mistake again.
Now I use the 5.2 buffer and have had great success.
Drinking on the keg: BPA, Brown Ale, Dry Mead, Wee Heavy aged on Oak, CAP
Drinking in the Bottle: