Quote Originally Posted by jcnkt_ellis View Post
You need an anerobic zone (low oxygen content) for denitrifying purposes so, imo, 2 inches of LR rubble below the sand bed would destroy that zone. 5 inches of sand, no rubble, imo, would work best. The idea, as I understand it, is to keep from using too fine of a sand, or too deep of a bed, in order to prevent an anoxic zone (no oxygen content) from forming underneath the anerobic zone.
Are you sure that is correct? I'm of the understanding denitrification only occurs in anoxic zones. Anaerobic is the biological reaction of organisms living in anoxic zones.

I agree about using sand and not rubble. Good live rock (read: very porous) can also provide many anoxic areas for denitrification to occur. This won't occur in rubble like it would a nice piece of LR.