Hi,
Usually, the DSB is about 4 to 6 inches in depth. Approximately 1 lb of lr per gallon is usually a good guestimate, but it depends on how you want to aquascape and the type of live rock you use. I would buy 15 lbs of lr and see how it works out. If you need more, you can always go back to the LFS.
It is better to aim for quality live rock rather than quantity of live rock. J&L sells fairly good live rock.
http://www.reefcorner.com/reef%20keeping_101.htm
- Victor.
[ 03 January 2002: Message edited by: reefburnaby ]