Originally Posted by d0 thy d3w
ummm...sorry if im hijacking..but whats a plenem?
the plenum system, was conceived by Dr. Jean Jaubert of the University of Nice.
A plenum system consists of a sand substrate, approximately 3 inches in depth, overlying a plastic grid, or plenum (such as eggcrate or even an undergravel filter plate). The grid is positioned approximately one inch from the bottom using sections of PVC tubing or another suitable material. The purpose of the plenum is to create a reservoir of stagnant, anoxic water beneath the sand, which promotes the colonization of beneficial denitrifying bacteria deep within the sand bed.
A layer of plastic window screening is placed on top of the grid so the sand cannot settle through the slots and fill up the plenum. The first 2 inches of sand are then added on top of the plenum followed by a second layer of screening. Finally, a one-inch layer of sand is added atop the second layer of screening and is seeded with live sand.
The screening between the upper and lower sand layers prevents burrowing organisms from disturbing the lower layer where denitrification takes place. The myriad sand-sifting organisms introduced via live sand to the top layer help maintain the proper oxygen gradient throughout the sand bed.
When a plenum system is functioning properly, aquarium water diffuses through the sand bed to the deepest layer, where any nitrate is converted to free nitrogen, which then bubbles up to the surface of the aquarium and is released into the atmosphere. However, if installed or maintained improperly, plenums have been known to trap detritus and release nutrients into the aquarium water or, in worst-case scenarios, to produce toxic hydrogen sulfide gas. Both of these problems can usually be prevented by providing vigorous water movement in the aquarium above the sand bed.
If setting up a plenum system sounds overly complicated to you, you're in good company. In fact, because plenums seem so unnecessarily complicated, they began to fall out of vogue a few years back.
That's not to suggest that plenums don't work. In fact, they work quite well when implemented correctly, and many aquarists still use them with excellent results. But over time, more and more aquarists have come to realize that they can reap the same benefits from a deep sand bed without the hassle of a plenum.
