in to deep

Looks like it could be root rot? Grab a box of fongarid from bunnings and mix it into your resevoir for a week then clean EVERYTHING incl resevoirs, soil testers etc can be hard to get rid of and will eventually kill your plants. Make sure your temps are below 30 degrees and your not overwatering them. they should be scavenging for water in veg stage so the roots dig deeper

yellow drying out leaves curling up, is likely root rott. pictures are unclear. You need to fix the cause of the problem (likely temp) or it will reoccur. Also keep your res out of direct sun as it creates a breeding ground for bacteria. Grab a bottle of cannazyme from your local hydro shop too it will eat away at the dead roots

Clean everything with bleach also. It is a fungus infection, which is hard to kick. Same as humans. Its like tinea - for plants

Last comment - CLEAN EVERYTHING - THEN ADD FONGARID. my mistake!

try letting your medium dry out a little too mate until you get things under control.

how often do u water?

is that a water reservoir in hte tent? if so wont it create humidity under lights?