For some, the concept of "building the water" is trickier and some brewers don't want to buy all of that distilled or RO water. Of course, some brewers HAVE to do this because their source water has enough issues that there is just no way to doctor it that much. BrewBama, by starting with distilled or RO, 15-25ml of acid would absolutely sound like too much to you. I have always used lactic acid and for me, about 4ml in the mash and about 1ml in the sparge is generally good and I need that amount because my otherwise-modest water numbers still contain 140ppm of bicarb. As for Jay's OP... if a piece of software tells you how much to add then it should get you in the zip code and it would depend on the acid you choose. I have never used phosphoric but I have always heard that it is "flavor-neutral". For lactic acid, I had seen a rule-of-thumb that you should not go more than 1ml per gallon of water used in the batch because you will have a flavor impact. I think that if you dialed it in just right, you could actually get a beneficial *acid snap* from the lactic acid that might make a beer more refreshing. As with anything else, the best situation is for each brewer to experiment and determine what all of these steps do for YOU and your tastebuds.