ask him if he recently sprayed plants (foliar feeding), evaporated water can leave behind concentrated mineral salts. This typically looks like fine, white crust or residue and does not grow or spread

WinJr63 said:

ask him if he recently sprayed plants (foliar feeding), evaporated water can leave behind concentrated mineral salts. This typically looks like fine, white crust or residue and does not grIts odd that its one plant out of 16 or 17. I moved that one out of the main tent and put it alone in his 2x2 and moved another plant in its place.

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What makes me stop and think is that its one plant out of 15 plants. I moved that one out into a 2x2 just to be safe. I moved another plant in its place. Might be an odd airflow area or something. I will see tomorrow, when i come over for checkup. Going off of his last log entry, he did not spray anything but i will double check with him, i hope tonight.

could just be perlite

That looks like stuff sitting on the leaf, not the leaf itself failing. If it wipes off clean and the tissue underneath is normal, I wouldn't treat it like bugs or mildew yet.

An ultrasonic humidifier with tap water can definitely leave that white mineral dust. The minerals ride out in the mist and dry on whatever leaf happens to be in that airflow path, so one plant catching it more than the others makes sense. The bigger chips in the pic could also be perlite or dry topdress dust that got kicked around, especially if he had a fan moving across the pot after amending.

I'd wipe that leaf with a damp cloth, check the nearby fan blades/tent poles for the same white crust, and find out what water is in the humidifier. RO or distilled water stops most of that. Also don't aim the mist straight into the canopy. If it doesn't come back after that and the leaf stays clean underneath, it's just residue, not a plant problem.

Humidifiers will definitely leave a white residue if you don't use distilled or r.o. water.