"dust" that's lighter than powdery mildew

Sieht deine Dusche auch so aus? Wenn nein ist es Mehltau. 😉😎

Full on powdery mildew!

it's the type of humidifier.. one of those misters or atomizers? those leave nasty films on everything, not just plants. the normal humidifiers won't do that even with tap water.

Good point on the humidifier. Cool mist humidifiers that use ultra sonic waves to mist the water into air will leave mineral deposits on things if you use tap water. Most of them do not work with distilled water or it damages its element in the humidifier. I find they tent to stick to things that are statically charged like TV's plastics and metal. vs plants. If its not a cool mist one and works by wicking water across a fabric like medium and a fan blows on it or heating the water to steam, it will no do this. If you have been foliar feeding with nutrients and using tap water this could be buildup of said minerals or the feed in the solution. If you recently installed a new filter in the tent it could be from it. If you have done a lot of moving or cleaning or painting in your place where the tent sucks air in from, this could be it. drywall dust maybe? If you been cooking lots with cooking spray or flour this could be from it. If you have a lot of forest fires close by and the air is ashy, this could be from it. A lot of this is assuming you have air movement in your tent pulling in air from the outside. If none of the above applies to you, and nothing has changed inside or outside the growing envirment, I am more inclined to believe it is WPM. Good Luck!

If you are running a humidifier it can leave a whiteish color on your leaves.