I would add the number onto your total. If you want 400 ppm....do your 400 and then add your other numbers on after that (400 plus your ph up, tap water, etc...) If you find that you are having to adjust your ph too much and it's making your number too high after awhile then you should consider using something like RO water which tends to stay more stable and not jump around as much or do more water changes to compensate. After adding things for awhile your number WILL get way up there and you can lose track of which part of your total niumber is nutes or additives or ph down etc..and that can REALLY mess you up.

Kush if I am misunderstanding your question I apologize and feel free to keep pounding away until you get it into my head.