http://96.31.86.198/vbulletin/forumdisplay.php?f=47
Just one of the threads from our superb reference library.
Yes, your correct that sand does have a large area for bacteria to colonize, but a dsb is not required for that purpose.
FWIW, many of us run bare bottomed and just use live rock for the same purpose. One theory is that if the tank/bottom is kept clean, less waste can decompose, thus less waste to create ammonia......nitrite.....so thus less nitrate.
Bioballs are extremely good at what they do, which is converting ammonia to nitrite and then to nitrate. Problem is without some form of denitrification, getting rid of the nitrates.