First leaves

Looks to me like your light may be too close and your either over or under watering them. Usually over watering in most growers cases. Just strait water at this point till there a bit bigger too. I’ve never grown in coco but I RDWC in clay pebbles and I start them in rock wool with strait water for at least the first week.

It looks like the internode distance is non-existent. Your lights may be too close. Seed should have power for ~10-14 days on its own, but with coco you must provide all the nutrients. as long as you get ~20% runoff, you won't build up anything in the substrate. So, feed a balanced diet each time you irrigate in coco. Do let it dry a bit between irrigations. Maybe, not an entire 1" like soil, but at least let it change colors up top. Learn the weight of the substrate when it is sufficiently dry yet not wilting. Especially early on, this will encourage a substantive root system from which you will benefit greatly in flower.

She needs a ph of 5.5 to 6 with 5.8 being the sweet spot for veg. You need to feed right away at 400 ppm 0.8 ec. Increase 100 ppm every week if your seeing good growth. 800 ppm 1.6 ec is around your stopping point. Cheers