Maybe a more pertinent question would be 'is a DSB necessary'?
There is a lot of discussion on that earlier in the thread( see posts nos. 250 to 350).
IMO, deep sand beds are not necessary ;nor inherently harmful when maintained. They can be fun for those who like the sand critters and microfauna they afford and are necessary for certain animals one may choose to keep like certain anemones, burying fish (some wrasses, jawfish etc) certain inverts like pistol shrimp , nausarius snails etc.
From my post #259
I've used and use shallow sand, deep sand and bare bottoms. There is no scientific reason of which I am aware to favor one over the other; they all require maintenance.
It is more of an aesthetic choice.
If you like the look of sand use it and clean it periodically,replenish some with new fauna bearing sand from time to time and it should do fine for a very long time . If you want to keep critters that need deep sand like certain wrasses and anemones ,using sand beds of appropriate depth for them is a necessity
Deep sand beds lost some of their allure a a biofilter , when I realized the bacteria performing denitrification are facultative heterotrophs. They live in the presence of oxygen and when they exhaust it in a given location they turn to nitrate for it facilitating the formation of N2 gas from some of the freed up N which exits the tank. If there is left over organic material and both oxygen and oxygen sourced from nitrate are exhausted,sulfate reducing bacteria take over.
This means denitrifying bacteria can do quite well in shallow sand or even on bare surfaces . They even create hypoxic conditions in their mulm where anaerobic activity occurs;ie, using the NO3 for oxygen. So, denitrification via assimilation of dissolved nitrogen as these bacteria grow and nitrate reduction to N and N2 occurs in the top half inch or so of the bed. Not much happens down deep for denitrification since these heterotrophic bacteria need a source of oxygen organic carbon, nitrogen and phosphate to grow and not much moves down there via diffusion, a relatively weak force or even advection a bit stronger but still inadequate force. Not much organic carbon,oxygen, nitrogen or phosphate will get down there fast enough to encourage much deitrification; nor much worry about sulfate reducing bacteria taking over and producing H2S since the sufat reducers need the organics too. In fact ,ime, you can find just as much evidence(black sufides) of anoxia and sufate reduction activity in shallow beds of an inch or so asanywhere else.
Overall, a shallow bed reduces nitrate a about the same rate as a deep one since the action is near the top where the nutrients are. Thus , the choice about a sand bed is more a preference than a case of a good method vs. a bad one,imo
