Put 2-3" of hydroton into the net pot first then place your rockwool cube and fill the rest of the way.
The water line should be 1" below the net pot so that the bubbles breaking the surface splash the bottom of the net pot. For the first week you can dump 1 cup of nutrient solution a day from the top just to aid the plants until the roots hit the water. Once the roots hit the water stop top feeding and pour a few cups of RO/Distilled with
hydrogaurd. Tap is fine if not using
hydrogaurd.
After 2 weeks you can lower the water to 2-3" below the net pot and keep it there the rest of the grow.
For the first week you want about 100-150ppm of feed. And 5000 lumen for light. You can download "light meter" by my mobile tools dev to check this on an android phone.
Water temps ideally 68-70
Air temps depend on the lighting used. I'm going to assume LED. So about 80f
RH about 60-65% this is important as it will reduce the demands on the roots until they are established.
Do not point any circulation fans directly at the seedlings.
Are you running sterile or live? Meaning bleach/
hydrogen peroxide or beneficial bacteria?
What lighting are you using?
What water are you using? RO, tap water etc.
What nutrients are you using?
Let's start with that and go from there.