Actually distilled water has a low pH because of the atmospheric gases in it, so depending on temperature (temperature affects solubility of gases) at the time of bottling, how long it has been open, etc. you might get diff readings.
Anyway if you're using distilled water #1 step is calmag plus.
Then add nutes. Then test pH.
Most growers should be fine with their tap water BTW. Except for sulfur guy... you've got a problem