For starters, your growroom looks like a Radar Range. I'd ditch the foil on the floor. Especially if the 600w is 12" from the plants. (will act like a Radar Range, too) What are your temperatures?

What were you considering 'low' humidity? High humidity coupled with high heat promotes mold. Moisture can and will get trapped between leaves, and trapped or standing water (on or inbetween the leaves) is a bad thing.

How much worm castings did you add to the mix? Too much, and the soil becomes more muddy than usable. (suffocates the roots)

You can still OD a plant using organics. Although castings are organic and slowly release nitrogen...the more worm castings you add, more nitrogen is being released.

If more help is needed, fill-out the CanCom troubleshooting form. :thumbsup:
Rusty Trichome Reviewed by Rusty Trichome on . black spot, shadow Hi to everybody My name is Dan i have a problem with my 3 week old plants. I grow them under 600hps, 12inch from a lamp. I had a small deficiency of N few days ago, but that problem was sorted. Ph of soil is 7, water between 6-7 (do my best to reach 6.5). there was a problem with humidity so started spraying leaves with water for a night. I did it every night and started 3 days ago. I sprayed the well with a water. Today morning one plant got some black shadows/spots on bottom leaves. Rating: 5