ok well i googled dwc and found this that might help you its out the hydroponics indoor horticulture book "
The system relies upon an air pump and an air stone to bubble air through the nutrient solution to mix it, but also in the beginning to generate spray, so as to get the clay pebble medium wet in order to establish the roots through the net pot. Consequently, the water has to be high enough to saturate the clay pebble medium by means of getting it wet or even moist via the actions of the bursting air bubbles. Once the plant has established a good root system, then it is advisable to lower the level of water in the bucket so that some of the roots can be allowed to hang in the air between the net pot and the water level. The majority of the roots live in the aerated deep water, 24 hours a day. With 24 hours a day in mind, as the roots are constantly submerged, it is crucial that the air pump is on 24 hours a day. If the pump is allowed to be off for any length of time, the roots will suffer from being waterlogged and starved of oxygen." heres the link to the site its not the whole book just one page on dwc you can also google it if you need more help... www.hydroponicist.com/pages/p44-dwc-bubbler.htm