Ya that makes sense. I to am doing full volume boils as well. So when you drop your ph to the level you want, the grains won't drop it further? When batch sparging I'd build my water, then in the initial mash the grains would take the ph from 7.2 down around 5.3. Then when I'd sparge I'd adjust that water to 5.3 on with acid since when adding that to the grains they where already pretty much spent.