<a href=showthread.php?s=&postid=9045951#post9045951 target=_blank>Originally posted</a> by Angel*Fish
Mr. Wilson,
How long have you had it like this? I thought R.Shimek had said that without the proper infauna, the dsb would harden (becoming useless) and that, regardless of total sand volume, a 30g tank was the smallest footprint one could expect the infauna to be successful in.
Please know, I'm not trying to inform you - I've seen you around and am pretty sure you've educated yourself about what you're doing - I'm just wanting to hear another view, which you clearly must have. 
Don't worry at all about second guessing me, I'm here to learn just like everyone else. The good thing about this forum is it isn't over-run by experts that won't consider a new idea that stays from their conventions. That's why you see more new innovations born here than on any other aquarium forum. Science is our friend, but it is flawed, especially at the hobby end. We are the pioneers, so there are no right or wrong answers.
Unfortunately, this is a very recent idea that challenges such conventions. From my experience, it takes about a year for a sand bed to become fully functional, so the jury will be out for a while on this tank. The other factor that clouds the issue, is the tank is only a few months old, and has not accumulated nitrate as yet. I believe there are enough other nutrients for the life in the sand bed to develop, nonetheless.
On the plus side, the sand I used was at the bottom of a commercial live rock vat for about nine months, at a depth of 18". I'm sure it's saturated with orthophosphates, but nothing that phosphate remover can't handle. You have to take the good with the bad. One interesting find was some tubifex-like worms that live just below the surface. They borrow to a depth of about 5" max, from my observations thus far.
Denitrificaton is carried out by macro-organisms (benthic invertebrates such as serpulid & polychaet worms, tunicates, sponges, and zooplankton) as well as micro-organisms (largely anaerobic bacteria called pseudomonas). Both of these methods of denitrification occur on and in deep sand beds, and are of equal importance.
In the case of macro-organisms, they require a large footprint in order to establish enough sites for a stable, efficient colony, as Dr. Ron suggests. In the case of bacteria, it requires a deep bed for adequate sites and anoxic conditions. As such, a bacterial bed does not require a large footprint, but rather, a large hand-print (if such a term exists).
The growth of benthic invertebrates is fostered in a "Benthic Zone" as part of a "Duplex Filtration System", in this particular tank. The egg-crate structure located in the sump, provides exponentially more viable surface area for benthic invertebrates, than a sand bed can offer.
http://www.reefcentral.com/forums/showthread.php?s=&threadid=969713
I've read in other DSB threads that 22" is the maximum effective depth, but I don't know the source of that belief. Apparently, any greater depth has diminished returns. While I believe that life goes on at greater depths, it's plausible that the micro-organisms that we have on our live rock, aren't conducive to anything deeper than 22". True sand denizens from bona-fide live sand, may change this depth limitation however.
I haven't read Dr. Rons article, so I'm not sure if his 30" x12" footprint, standard is taken out of context or not. I think he's referring only to macro-organisms with the term "infauna". The solidification of sand is a chemical process, spurred on by biological activity and subsequent acidic conditions. Burrowing invertebrates cannot inhibit localized acidic conditions. They can break-up sand as it binds to certain extent, but not enough to keep-up and certainly not at greater depths. Solidification may be inevitable, and may or may not be detrimental.
Solidified sand is useless to benthic invertebrates, but I don't believe it to be adverse conditions for bacteria. The whole reason why many sand beds have been moved to a remote location, is to exclude sand-sifting creatures like gobies, stars and cucumbers, as they interfere with the anoxic conditions and stability of the bacterial colony. The DSB bucket idea is based on the exclusion of macro-organisms in the sand bed, with the focus on micro-organisms (bacteria).
