Deep Sand Bed
Posted: Sun Jan 15, 2012 1:45 am
Yes, FW DSB and/or plenums* do work. I use such routinely.
*Plenums are simply restricted depth DSB which have a plenum layer of water beneath the substrate layer. The deep layer of water allows ready diffusion within the plenum, but no direct connect with the water column above the substrate. Plenums tanks, properly set, cannot generate methane or hydrogen sulfide as can DBB due to their restriction of the ammonia to DO (dissolved oxygen) levels above that require for generation of those toxic gasses. This blocks some of the worst mis-handlings possible with DSB and markedly reduces the problems when unsuitable fish are housed in such tanks.
But, DSB or plenums are not quick or particularly easy to establish. They can be stable over more years than most hobbyists maintain their tanks. I consider ten years or more stability to be quite good and should be routine. To me setting a tank for less than 10 year operation is a waste of time and materials. No, I do not keep all of my tanks going for at least 10 years, but that is the figure I use when designing them.
IME, FW DSB or plenums tend to require three or four to eight or more months to mature, versus 2-4 weeks for conventional aerobic bacteria biofiltration. But in fairness, DSB or plenum tanks do a heck of a lot more waste processing than just ammonia oxidation to nitrite and nitrite oxidation to nitrate. DSB or plenums can and do reduce nitrate to ammonia and that ammonia to nitrogen gas - which diffuses or bubbles out of the subatrate to the atmosphere. Thus these are the only FW hobby tanks which have more than the short ammonia to nitrate pathway available and the only FW tanks which can dump nitrate without water changes and/or plant or algae mass harvesting. But no, they do not IME dump enough nitrogen gas to elimimate the need for water changes. DSB or plenum FW tanks are the only FW tank IME which can approach SW FOWLR - skimmer + macroalgae rerfugim in reducing the requirement for FW water partials. IME, the FW setup is not quite as effective as the SW one. I suspect that difference or gap will be difficult to close fully, as the skimmer function is simply not available to us in FW. Despite Ms Walstad's writing to the contrary, I do not and will not ever operate any tank by her supposed "scientific" techniques. But that is another discusion entirely.
I also disagree with the author of the WWM site article in that I would never suggest that any hobbyist who is not an advanced microbiologist at least should evet consider adding Tubifex worms to their tank. The potential hazards far outweigh any possible use of such high-risk critters. NIMFT, not ever.