Turtle is right. I grow from seeds with rockwool cubes and little netpot. If the plant has got or no roots, it's the same. The popping bubbles damp the rockwool cube ( if the level of water is high enough ). It's better to wait the roots to go out from the cube before putting it in the DWC system. Rockwool keep dampness too much, and i notice better progress to plants that have been put in DWC once roots out than the other ones. If they have no roots out, you better feed them manually, once or twice a day.
Fhydro