I add calmag and a tiny amount of masterblend. I have well water with 8.0+ as normal pH. I also have an RO filter and have used that. I also tried with distilled water but I just suck at it...and the pen seems to jump all over...goes from a lot too high to a little too low...so I add more water and then it’s way too high again. dying here...Are you PH'ing plain water or a nutrient mix?