Root Structure in Shallow Water Culture.
In a normal DWC the roots are usually mainly totally submerged, hence the need for extra air. Obviously the root system goes all through the clay balls, but here is what it looks like in the Shallow part of the SWC in both of the two examples. There is a fairly solid mat of roots which sit submerged in the nutrient, like a DWC, then they fill up the available air space, all the while not interfering with the pump. Also see how the clay balls float to the surface ensuring almost 100% recovery of medium. The expanded is clay is dearer than other inert substrates but it's cheaper in the long term and better too.