David’s tank is a custom 1,200 gallon “L” shaped aquarium housing some breathtaking specimens of both coral and fish. The total system volume is over 3,700 gallons including the refugium, sump, and other equipment.
http://www.youtube.com/watch?v=OLRubZGWXiY
For more information on this tank, check out this detailed PDF outlining the tank. Also, this is an older article at UltimateReef.com but it gives a good overview of the tank and how the tank looked in 2007.