One tablespoon of 5.2 per 5 gallon batch and your water is instantly adjusted to the perfect ph of 5.2, no matter what your starting ph was. It will not add any flavors to your mash water whatsoever. 5.2 optimizes the enzymatic activity of your malt, helps to clarify the wort, and may even help to raise your starting gravities. Also, using 5.2 in the boil will give you more consistent hop usage, and will also keep hard water salts in solution, which will result in less scaling in your heat exchangers, fermenters, and kegs.
If you are doing all-grain you add it to your mash water - 1 tblsp per 5 gallon batch regardless of mash water volume. You do not need to add any extra to your Hot-Liqour tank or Boil Kettle.