I adjust my pH dropwise and re-test until it is correct, if I'm adjusting it at all.

That 2.5mL/90L is for a specific increase... if you need to increase LESS, then you use less, etc.

Unless your tap water is really bad, just use room temp water right out of the tap, then add nutes, then test pH, and if it is off, adjust accordingly. I think you are adding an extra step, if I am undesrtanding you correctly.