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 progresses from tiny yellow-dot stippling, to more dot stippling, then to stipples growing in size, and finally covering the whole leaf. (It's 100% not spider mites, by the way.) The stipples generally seem to follow alongside the veins, but not exclusively. On the underside of the leaf, it looks like the stipple is actually a very tiny eaten area, that expands -- both in the number of them and the size. I took an extreme close-up that shows this pretty clearly. I can see no insects or eggs under multiple magnifications, from 2x to 100x -- and I've looked fairly often. If it's a pest, it's one that is invisible at 100x, and crawling all over my grow room. The room is going into the latter stages of flowering, but everything will be the same for the next grow -- so I better find out now, before I damage another crop! Thanks for any help! ~jessie PS: Links to the HI-RES pictures: FileDen.com | Free file hosting and online storage FileDen.com | Free file hosting and online storage FileDen.com | Free file hosting and online storage To supplement the pics, here are the grow details: MAIN: 15 plants, flowered March 1st, 2010 (after 6 weeks of vegging) STRAINS: AK-47, White Widow, Ice, Chrystal, LA Woman (all from seed) GROW ROOM: 6' x 8' SCROG GROW METHOD: Hybrid Drip/DWC. Six self-contained totes, each its own reservoir. LIGHT: 2 x 1000w HPS (air-cooled vents) NUTES: 800-1200ppm, Lucas Method using General Hydroponics, and I don't use any other supplements (when I get more knowledgeable, I'm sure I'll start experimenting . . . ). TEMP: 70- to 90-degrees HUMIDITY: Recently upped to 50%, from 30-ish% PH: Mid 5's, checked regularly. CO2: None now. Tried for exactly one day: the room is heavily vented. Maybe next grow I'll figure a way that doesn't break the bank. My main diagnostic theory is HEAT STRESS, possibly compounded by low humidity. The room is really comfy now (mid-seventies, 50% humidity, well-vented), but for a good 4-weeks it was bad (mid- to upper-80's, 30% humidity). My books on growing don't mention heat stress causing dots like this. My minor theory is some sort of nutrient lockout. I use tap water run through a multi-stage filter, but it's not distillation -- and the tap water here is hard (about 200ppm). The thing is, I've already gone through two grows using this water and nothing like this happened.