Coteledons feed plant for a couple of weeks .....
Are you determined to start them in coco ? You might have better luck with
promix and perlite with a little bit of organic nutrient , like some worm castings or
foxfarm soil diluted in the mix for a more uniform gentle feeding in early growth , figuring out how to manage coco and feed new sprouts can be challenging , the t 5s are a great start , your seedlings are suffering from environment issues and wet / dry nutrient issues .....
Raise the light , remove heat pad , back off on nutes , be patient , they will perk up , but seedlings are sensitive and if you shock em from the start you can run into problems
If you gave them to me , i would get them into a different medium , maybe some coco guys can chime in , good luck
What genetics are they ?