Planted Tank Guru
Join Date: Jun 2004
Location: Baton Rouge, LA
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.