Are you spraying your plants with hard tap water?
I don’t mean to hijack the thread but your question hit a nerve. I have very hard water.....but it’s ph isn’t crazy high (around 7.1) and the PPM is 140’s.
The humidity here is very low this time of year and I have to run 2 humidifiers just to get the RH up into the 40s...which is fine for me now as I’m in mid flower and don’t want higher levels. I noticed a white, almost powdery film on the side of my Mylar foil all around the small room. I took a wet towel and wiped it off for the most part, but I couldn’t figure out what the hell it was or where it came from. Then your question made me realize I’ve been running straight tap water in my humidifiers. Am I right in thinking it’s coming from the hard water?? Better yet, am I none the wiser for learning this?