I've been adjusting my water for many years, primarily using Bru'n Water, and I've never seen a need for 40 ml of 88% lactic acid in eight gallons. I would guess water that required that much adjustment would be unfit for brewing and perhaps unsafe for drinking. It may be right, but that's far enough out of line that it demands investigation. I strongly recommend that you download Bru'n Water (https://sites.google.com/site/brunwater/), read the instruction tab (twice) and recalculate your pH adjustment. Yes, it's a complex subject, but with a minimum of study you can make it work reliably.