A
deep sand bed (sometimes abbreviated
DSB and
also called a "plenum") is a
filtration method used in some saltwater aquariums. A deep
sand bed, like the Berlin Method, is designed to cultivate
anaerobic bacteria in the bottom layers of sand, which can
convert nitrate to nitrogen gas, thus eliminating the toxic substance from
the water.
A deep sand bed is generally defined as a bed
of fine sand at least 4 to 6 inches deep. This depth is
necessary to ensure that there will be enough water
receiving poor circulation. An established deep sand bed is
actually made up of
live sand which, like
live rock, is full of bacteria and other marine
organisms such as worms, crabs, snails, and stars. These
creatures dig through the top inch or so of sand in search
of nourishment, which helps circulate water much deeper into
the sand than would be possible without their aid.
Deep sand beds can be made of any material, but typically
fine or "superfine" sand is used, having a size anywhere
between 1 mm and 0.05 mm. A larger size might allow for
better circulation, which would in turn require a greater
depth. At the same time, the larger particles could be too
heavy for the worms and other inhabitants to move around,
which would limit their ability to help. Lastly, very large
particles (2 mm or larger) are very likely to accumulate
detritus, which would necessitate periodic siphon
cleaning. A well-chosen fine grain sand, on the other hand,
will create a deep sand bed which may never need cleaning.
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