Have you been foliar feeding or spraying the plants on a regular basis? if so...stop till you know that it's not causing the issue.
Do you have fresh air supply and fan's on 'em at all times?
Rusty Trichome Reviewed by Rusty Trichome on . very odd problem I'm not an expert at this but I have been doing this for awhile and I've got something that I've never seen before nor do I have any idea where to start. I have to apologize, my camera is not taking good enough pics with any focus to see the problem.... You know when you accidentally get a drop of Ph down or nutes on a leaf and you get that little whitish/greyish spot on it? Well, I'm getting something that looks a little like it and originally I thought maybe that was the issue but now I'm Rating: 5