Just use a two large needle wheel pump (Sequence Reeflo Orca needle wheel pump) with a venturi valve attavched to the pumps inlet. It pumps about 2500 gph of water full of minature i airbubbles. Use 4" diamter PVC pipe at the bttom sides of each tub set up in a rectanglular layout. The pipes interconnect each tub and thesecond pump is at the opposite end of the rectnlular tub layout so that thw air filedwater is pimped in acircle through te bottom of each tube. The small bubbles rise to the waters surface as the water is pumped through the systems. The pumps use about 90 watts each. Basically I just described a vastly improved under current system. Under current systems use a cheap Danner pump and airstones. Sad, but better than a typical DWC system. Reeflo Orca pump:
http://www.aquacave.com/sequence-reeflo-orca-needlebr--wheel-water-pump-1348.html No, at $300 each they are not cheap. But a Counter Flow system runs $1200.
To connect the pipes to the tubs use uniseals:
http://www.aquaticeco.com/subcategories/829/Uniseals/uniseal/0