I realize that I need to use distilled water when I mix my dry ferts for pps pro that I should add 20 ml of excel for 500ml. Should I boil the distilled water before i mix? I got this distilled water from walmart.
The main reason distilled water is used is because both the Iron EDTA in CSM+B, and Excel, break down at high pH. Most tapwater has high pH, so if you use that, your solution will degrade in the bottle.
Heating the distilled water a bit will make it easier to dissolve stuff in it, but it's not necessary to sterilize it through boiling. The Excel takes care of sterilization.