Leafs are getting light yellow/brownish

My plants are about 2weeks old, i have them in a terrarium with a fan and lights all layered with mylar. the tips of the leaves and edges seem like they are getting brown & yellowish is this from to many nutrients? not enough light?
any help is appreciated.
Thanks!!

Whats your light cycle currently? could also be from overwqatering, how often do you water ?

yea man it could be any one of those things including overwatering..

umm been watering abuot every 2-3 days and its on an 18-6 light cycle right now

What nutrients are you using and how much ? I had the same problem right after i gave them some i noticed the tips were brownish kinda burnt in a way. So it kinda might be that.