So then is the answer to use RO water?
aNs
I've always used R/O with DWC... hell, with everything I've grown in the last 10 years.
The only time I've had problems with DWC is when the tap water sucked so bad you couldn't even rinse the hydro gear with tap-water, without getting hydro herpes from it.
My temps have always been consistently around 68F... won't do DWC unless I can maintain those temps and ALWAYS try to put the air-pumps in a cold/cooler air spot.
No organics, no sugars, no snake oils. Just a shitload of bubbles and clean nutes.
Stay Safe!