02-13-2013, 08:06 AM
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I'll offer an opinion based on extensive study and some limited experience. So what follows is merely food for thought.
I think deep sand has potential in FW, just as it has in SW, BUT is dependent on an extensive "bio-collaboration".
> Sand grain size. Sand that is too coarse would have to be extra deep in order to create any real anaerobic regions. Sand that is too fine will likely pack and impede plant root growth and bacteria cultures. Pool filter sand is preferred by many proponents of deep sand.
> Rooted Plants are required to produce localized oxygenated regions and nutrient absorbtion.
> Substrate creatures like (California black) worms and Malaysian Trumpet snails work in the substrate food web.
> MULM is required as a food source for the biology that make deep sand work.
This can present a somewhat offensive appearance for many fish keepers but siphoning the surface removes the food necessary to "feed the sand critters".
> UNDISTURBED SAND - many that have experimented with deep sand somehow become convinced they need to stir the sand bed. This is very counter productive as detritus stirred deep in the sand results in putrid anaerobic decomposition, something we never want in our aquarium.
> Time - it takes many months to develop and culture the deep sand bed.
Just like a lot of living plants, deep sand does offer the potential to further assist in water purification and completion of the N2 cycle (that being nitrate conversion to nitrogen gas).
On the other hand there are some other considerations...
What if we take steps to prevent tank generated nitrates? That which is never created needs not be removed.
What is the objective in nitrate removal? - Even if we were able to process nitrates, although a good thing, what about the other pollutants in the water that get removed with the weekly water change? Admittedly, many organic compounds decompose into fairly inert components. However, there are some things that will concentrate and in time negatively affect water quality.
Footnote: I personally believe that with good filtration/purification, clean tank/filter maintenance, periodic use of 'chemical' filtration (e.g. materials like activated carbon and synthetic scavenger resins that adsorb impurities) and proper feeding ensuring that stock is not over fed producing excess waste, AND maintaining an appropriate stock level/bio-load, weekly water change volumes 'could' be effectively reduced. HOWEVER, partial weekly water changes (lets say at least 10%) remain essential in maintaining a healthy aquarium. Like rain in the amazon, the WWC removes used water and charges the system with new fresh water that stimulates all of the tank biology.