small seedlings????

I germinated them in rapid rooter. 2 weeks ago I put the rapid rooter plugs in net pots, with phed tap water (6). they are about 5cm tall with 4 2.5cm leaves and the stalks are so skinny and fragile im afraid to cover the tops with hydroton. I have grown in soil before but the plants were 4 times the size by now. any suggestion I must be doing something wrong. I wanted to veg them for 4-6 weeks but this rate 4-6 months
Lights: 324 watt t5 5cm from the tallest one
113 L/56 L dwc totes
medium: rapid rooter plugs in hydroton
Environment:15 -27C
30 -40% humidity
No nutes yet
water temp???
ppm????

maybe because no nutes? in soil nutes are almost always available

**update** I gave them some nutes 4 days ago and checked my water temp it stays at about 20.2 C despite temperature fluctuations still no significant growth. any tips or ideas? should they be this small at 20 days??

almost 4 weeks old they grew some they are about 10 cm tall any one know how can boost them some?
temps a little more stable 18-24

sometimes ya just have to give up I still wonder what went wrong other than genetics (bagseed) can't play that big of a factor. the other girls are doing fine but I had to pull him/her