Dreaded Hermie speaks the truth here.
I prefer tap water to RO water for my hydro work as it's more stable. I just add my "target" EC to the tap EC for the final EC product.

M.P.
MerryPrankstr Reviewed by MerryPrankstr on . RO H20 + Cal Mag Plus = Unstable pH Hello farmers having some pH problems. Here's the setup... 20 gallon tote with 6 airstones for a bubbling DWC for seedlings. Inside the 20 gallon tote there is currently 15 gallons RO H20 w/ 75 mL of Cal Mag Plus (5 mL per gallon Cal Mag Plus). There is nothing else in this reservoir. Air temps are around 68 degrees farenheit and water temps are between 63 - 68 degrees farenheit. Rating: 5