You want to remove the wrapping on your rock wook cube, your choking it because the roots want to grow out the sides as well as the bottom! Also fill in the net pot with hydroton or perilite such that the top of the rockwool cube is also coverd up.
Whats the water pump in the bottom of the 5 gallon bucket for? Are you drip feeding as well as blowing bubbles? You can get rid of the drip feeder after the roots hit the water, thats what I do anyways. Good luck and happy growing!