why are we running DSB and is it for the right reasons

[powerreef]

Its a tough debate. DSB's are very forgiving for the new tank and new user. They give the reefer an easy way of avoiding maintenance and not being punished.
I fall on the Nay sayers side, but I do see some advantages to a sand substraight. People who use DSB's use them for 2 basic reasons. One is for denitrification and the second is the bug life that it contains. These are 2 good reasons but a DSB is not needed to achieve them. I will elaborate a little more below. The inherant problem with DSB's is that they dont process everything. In reality they only process nitrogen based products, this would leave everything else unused and thus still in thier. Because our tanks have a bottom, this unused stuff piles up. As it fills (and nobody knows how long that takes, it has to do with feeding ammounts and husbandry) it drives the anerobic nd aerobic zones higher in the sand column, and because thier is a surface the upper zones just keep getting smaller and thus loose thier filtering compacity. Another huge problem and probibly the one most reefers encounter is the inability to deal with Phosphates. Concidering that all life in the bed carries phosphates and the simple PHosphate cycle of an argonate based sand Phosphates will leach back into the tank. This is where you see folks having problems with patches of algae here and cyano over thier and so on. An endless cycle of algae blooms.
Nitrification and 99% of all bug life lives in the upper aerobic zone. All bugs with the exception of bacteria/enzynes and protozoas need oxygen to live. So here is the way nitrification works in your bed.
dinitrogen is reduced by reduced dinitrogenase (which uses a coenzyme containing iron and molybdnym to carry out its reducing activity) to form dinitrogen dihydride (requires reduced dinitrogenase, 4 protons and 4 electrons)
dinitrogen dihydride is reduced by dinitrogenase to form dinitrogen tetrahydride (requires reduced dinitrogenase, 2 protons and 2 electrons)
dinitrogen tetrahydride is reduced by dinitrogenase to form 2 ammonia molecules (requires reduced dinitrogenase, 2 protons and 2 electrons). Sounds complicated by its a pretty simple process with nitrate as the end product. From here nitrates are brought down to the anerobic zone (a thi layer of both mixed oxygenated and anoxic zone. Now bacteria once again reduces nitrates to nitrogen gas. The bacteria that do this are facultative (means they consume oxygen first and when it runs out they go after nitrate ..basically). So once it is converted to gas the movement of bacteria and critters allows the nitrogen to off gas (the little bubbles you see in the bed).
From this point thier is nothing in your bed that does anything for your reef tank. These 2 zones can be fully operational with only a 1 1/2 to 2 inches of substraight, using either oothilic or even CC.
Now on the down side of this in the deeper zones we have a suphur cycle, iron cycle and a varity of nasty operations done by infuana that will never benefit the tank in itself. So why have it????? Thats why if one feels the need for sand in a tank 1 1/2 to 2 inches is more then enough to do everything you want. When the build up of things that are not nitrogen based occurs one can simply syphon out the entire sand bed, and thus rid yourself of any long term problems. People argue that it will kill your nitrate reducing bactering, this is simply not true, they are facultative and will simply consume oxygen until once more it runs out in the bed (very quickly) then they will revert to nitrate once again.
On the remote DSB, been thier done that. Bottom line is that it is not needed. A shallow bed will do everything you want, with out having to do the big nasty down the road. Also if you choose to set up a remote make sure you have a real long ammount of contact time, or it will turn into a settling tank in a hurry. IMHO a remote refugium with a 2 inch bed of sea floor and macro's are more then enough to take care of any dentrification you will ever need. Lets not forget the L:R that does the same thing .

Anyway sorry for the rambling

MIke