Properly fill-out the troubleshooting form, and we can get a better idea of your situation. But with the info provided, looks to me like either nutrient burn or micronutrient burn.

You mentioned not using additives...does this include foliar sprays? How about Superthrive or one of the many bulking agents? Perhaps an iron or magnesium suppliment? Looks like repeated overdosing, but would need more info to confirm or dispell. My guess is magnesium or Superthrive OD. (just a shot-in-the-dark guess)

Then again...I'm not a hydro guy, and it might be something as simple as reservoir temps or nozzle clog. :wtf:
Rusty Trichome Reviewed by Rusty Trichome on . Yellow Leaf Dots Spreading Completely Over Some Leaves (It's not spider mites) Hi All, I'm trying to diagnose this leaf problem. It's currently affecting almost every plant in the room, some significantly (half the leaves), others totally minor. It doesn't seem to have any pattern: the edge plants (least light, least heat) have it no more or no less than the center plants. I know there are a lot of factors to consider in diagnosing a plant problem, but maybe someone will know what's going on -- once they see the pics and read the post. The pictures show how it Rating: 5