what's happening to my 2 weeks old baby...

[Rusty Trichome]

Hi all

Hello

pre-lightmix soil I got at the growshop

Huh...? Is this a peat based mix? (potting soil) Is it pre-fertilized or ph buffered?

growing it under a 400w master son-t pia philips bulb with a reflector.

HPS? What distance from tops? The seedlings can't yet handle the lumens and heat like the larger plant. I'd raise the larger plant 6 inches or so (15 to 20 cm) and the light too if necessary. My 400w batwing I was keeping at about 12-16 inches,(30 cm?) more if necessary because of heat. My 400w glass enclosed hood was at 10-12". (25 cm?) For seedlings, about 24 inches. (60 cm?)

I use bottled water with pH 6 to 7 tops.

Best to keep your ingoing ph as stable and consistent as possible. Growth and nutrient uptake issues if not. What's wrong with your tapwater?

the temperature in the closet is a steady 27 degrees (80F) sometimes it gets a degree higher or lower but it's not for long. the first week I had it under light 24 hours a day but 4 days ago I started to do 18/6 lighting, and after I changed the lighting (6 hours of darkness overnight) I noticed that way the temperature at night in the growcabinet gets around 18 degrees (64F) because the light is off, when the light was on 24h it was a steady 27 degrees always. yesterday I got a fan to help with the airflow.

Try and keep the gap in temps as tight as possible without getting all anal and obsessive about it. I live in the desert, and my plants handle the heat of summer better than they handle the cold of winter. There are upper limits though. Me...I'd raise the temps at night a tad. Easier than trying to cool off during the day. This is insight, not a recommendation.

everyday I spray water around the cabinet to help increase humidity to around 60% but most of the times it's around 40% (since I added the fan I noticed that it's steady around 50% but I have seen 30% before but not for long cuz I would spray water around, I use a fine mist sprayer)

Some folks fret over low humidity. In my region, low humidity is less than 8%. But if properly watered, they can usually provide their own moisture, (roots) and the soil evaoprates moisture, raising humidity a tad anyway. Only time I ever spray is to correct deficiencies.