A gentle fan moving the air around the plants will strengthen the stocks.
What temperature (color) of light are you using?

Seedlings in grow rocks already is not really a good idea. If you had rooted them (even from seed) until you had 4 sets of true leafs (then you are in the vegetation cycle) at that point then you have a true plant. The stems will always stretch a bit and you can use that when you transplant them to get the roots deep in the net pot the put the rocks in on top. That will hold up the thin stocks and give the plant a good base to grow from and provide strong support for later on in it’s life cycle.
Zandor Reviewed by Zandor on . Many Questions? Ok what's up everyone the first question is can someone tell me if these seedlings are stretching too much?(pic below they are about 7 days old nirvana's misty strain. I'm also setting up tubs for the vegging area I'm sqeezing about 20 in each 2x3 tub I think they are 55 gallons, 3 inch netpots. I want to set up tubs for the flower room which is bigger so I want to put them in bigger tubs with 6 inch net pots. Is it possible to switch pots in dwc. Or can I just ride it out in the 3 inch pots. Rating: 5