Yeap! I'd just like to update you guys and anyone else who may come across the same problem.
My mistake was indeed the soil, and the jiffy cups. The soil was way too strong, bio bizz all mix, dutch stuff, pretty much cooked my seedlings because it was heavy in nutrients.
The jiffy cups are just an oven under a 600w hps! It just absorbed any moisture out of the already shit soil, and then the light evaporated it.
What i've changed, bought way lighter soil, with smaller perlite
Lowered my ballast to 400w, and bought small plastic square pots to keep the moisture in.
ALSO, i've got myself a nice bunch of seeds. In the room now: 2 Lemon Diesel (Emerald Triangle seeds), 4 Liberty HAze (Barneys Farm), 1 Blue Dream (Dinafem), and the 1 misty original that survived my desert-like atmosphere a few days back and oh boy how she's flourished!
About to update my grow diary with pics:
https://www.rollitup.org/grow-journals/629269-scrog-grow-original-misty-bubba.html
Thanks for all your help !