Originally Posted by boredatwork
The advice I heard is add an appropriate amount for the volume of your mash, and the add the remainder for the full pre-boil volume to the wort once in the boil kettle.
This guy is exactly right.
Add the appropriate salts to your mash, add the sparge water salts to the BK prior to the boil.
If you arent adding PH adjusters like lactic acid to your water, then you may still want to use something like Buffer 5.2