The In Box a discussion of sand beds between Sam Gamble and Eric Borneman

Hello Sam: I have an observation that correlates with talks I have had with several well educated people in this area. We are not convinced that the sand bed is entirely anaerobic or anoxic, because of the relatively shallow depths involved. In the establishment of a recent plenum system (thought not by any means the first), a number of aiptasia anemones propagated in the plenum and moved slowly toward the reflected light of the glass and up through the sand bed over a period of months. Amphipods are regularly seen in the plenum, as well. The most notable finding was that of an astrea snail, with substantial mass and metabolic respiratory needs, who was maintained by accident in the plenum for over four months before death ensued (probably from lack of food). The oxygen transported through a gradient in the bed is obviously great enough to support life. While this gradient certainly should exist, it leads me to question the amount of oxygen in the bed....in other words, there is an obviously high level of O2 in the plenum...is it high enough to correspond to levels within the sand bed (over 4" thick throughout) that are not truly anoxic or anaerobic.

On another note, I have been using live sand beds for over three years. The first was simply live sand on the tank bottom. I have followed with sand beds composed of dead aragonite and mixtures of both. There seems to be very common view held that the "dead sand" will soon become live as microfauna from the rock populates the sand. I have to disagree. All my live sand beds have been highly effective denitrators and processors of organic wastes. My first live sand (1" on the bottom) was very efficient. However, the "dead sand" bed became a detritus trap and was a constant source of cyanobacterial and diatom growth. It was also very inefficient at denitrification, and my nitrates rose rather than declined. Poor set-up? Doubtful, because new systems just confirmed this finding.

I know now that the dead sand never does become truly "live" as has been reported. Over a long time, it may become more-so, but I do not think it will ever become exclusively live as is true of the "real thing." In fact, my experience leads me to think that the problems that may occur while such a pseudo-live sand is being formed will outweigh the benefits. Similarly, seeding with a small quantity of live sand will not provide the microfauna found in a large amount of live sand, simply because of the statistical probability of finding much variety of life forms in a pound or so of true live sand. While bacterial populations will certainly occur in either system, and some microfauna does indeed pervade the dead sand from the rock, my experience is that there are far too many beneficial worms/microfauna in true live sand that are responsible for a great deal of food and waste breakdown that are indigenous to sand and not rock...this would be apparent by any logical thought about microcosms. The breakdown by these organisms facilitates the ease of denitrification by bacteria, and thus makes an important statement regarding sand bed filtration. This was further proved by several sand beds I have set up using "live sand" from poor suppliers that turned out to be not much more than beach sand...i.e. it was not collected form reef areas that contained much microfauna at all. I had similarly poor results, though less detrimental than with the use of the solely dead aragonitic material. Thus, it seems to me as if there are very definite grades of sand in terms of quality, similar to those now recognized and seen in live rock.

My current system is a highly effective bed composed of sand from sources that I have found to be of excellent quality...although none seem as "live" as my very first shipment of live sand. Odd, but understandable given the profits of this "new" system that is attracting demand by less experienced hobbyists. And, of course, supply needs to be met, by the already expected poor collection methods by unscrupulous collectors in an attempt to lower cost and provide "live sand" to those who don't know any better.

So, this is my report on the findings of long term usage of different methods of live sand NNR filters. I think it may contrast sharply with a lot of other reports, but I can assure you that my experiences are not coincidences....

Please write back with your comments. Thank you.

Eric, Your statement that your not convinced that the sand bed is not entirely anaerobic or anoxic, is correct. However, depth is not the determining factor alone. Our recent trend in aquarium filtration is using sand beds specifically constructed to provide environments for increased natural microbial mediation. The goal is to properly maintain as many compounds and elements as possible at

natural and desirable levels. The idea brings our attention back to the cell and its activities. Our ability to use microbial populations of cells, stems from what we measure as ecological variables, i.e. physical and chemical factors and the properties of the microbial populations themselves, such as their distribution, densities, metabolic requirements, and activities.

The aquarium and the sand bed change constantly. For an ecosystem to remain healthy it must continually change or be in flux. If you are trying to maintain an aquarium you must consider the main culture you wish to preserve and then understand that countless microscopic events must happen to maintain the macro cultures. The best way to understand the system is to understand the single cell and what it needs to promote its equilibrium.

So, your statement the sand bed is not entirely anaerobic (cell respiration where degraded molecules occur without the participation of molecular oxygen) and anoxic (respiration with reduced amounts of molecular oxygen) is valid. To characterize the environment as ONLY anaerobic, lends itself to the term "obligate". In other words the presence of oxygen would harm the cells in that environment.

Since reduced oxygen levels are periodically found in the sand bed and plenum, facultative is the accurate term. It is also the facultative microbes that have been credited to doing most of the metabolizing. Keep in mind the environment is in "flux" also favors facultative traits and activities of cells.

Your plenum that contains livestock is not a typical situation. Probably not a desirable one either. It may dramatize a drawback for plenums exposed to light. In the previous articles I used the analogy between plenums and a dark basement. It depicts a dark storage area, to collect unused and discarded substances to be recycled for later use. You apparently have the cellar door open. Light loving organisms are living in it and aren't noted for being able to dig burrows.

It has allowed for extraneous sources of molecular flux. The feeding algae eating snail, shows that autotrophs (plants) are present and quite possibly heterotrophs as well. The plenum is more typically an environment for chemosynthesis. Now go back to the first paragraph, about our ability to use microbial populations and the properties of their environment.

Light plus the avenue through the sand bed for the snail, anemones, and amphipods produces an environment not characteristic of a typical plenum. The autotrophs the snail fed on (4 months) produced oxygen by photosynthesis from light energy. The Aiptasia also contain plants, zooxanthellae. Close the cellar door and turn out the lights in the basement. It will encourage the properties necessary for desired microbial populations in densities, and distributions allowing more expected metabolic requirements.

Sand in nature is a sink for organic compounds &/or elements of organic compounds. There have been many studies done of ecological factors of environments that range greatly,e.g. reefs to estuaries and salt marshes. The substrate below the surface interface has the common characteristic of being a "sink" for all of them. Nitrogen compounds and phosphorous compounds are two good examples that we are familiar with that cause algal mats like the dreaded hair algae.

In nature there is another characteristic that goes with the sink concept; anaerobic. In our aquariums when nutrients diffuse and collect in the substrate (sand) it is usually associated with the tendency to be void of usable dissolved oxygen. Fermentation, not oxidative respiration is then the main event. When a system gets started out out of balance the "sink" ability that encourages nitrogen fixation like algae growth and organic accumulation are often seen. When a plenum'ed system is provided with a good start of microbes that fill the empty niche of the "dead sand", natural selection favors the production of a system that uses destructive denitrification, rather than assimilation of ammonia from nitrate. For sure Eric, when sand is used that is loaded with organic compounds and the less desirable obligate microbes, then problems occur. It will tend to become a lot like natural systems where anaerobic populations dominate the energy cycling pathways just beneath the surface. And that would look just like your evaluation that the dead sand never truly becomes live. How many desirable critters for our aquariums like to dig into an area like that? Fred worm to Ralph worm, " not me man, you go first".

However, if "dead sand" is topped with the types of bacteria that like an anoxic environment then they will colonize it without wasting any time. Now we're back to facultative versus obligate. They usually do so before it loads up with organic compounds to favor the less desirable obligate anaerobic condition. Like you suggest, the very reason to buy or collect good and reputable inoculating live sand. It's also the reason why I grow facultative sand in a facultative environment of reduced organic compounds that may have nitrogen or phosphorous in them (no commercial plug).

Would like to add to your point about microfauna; it's the cell and its metabolism that recycles the waste or nutrient compounds. The worms and little critters provide a function of transportation and added oxygen from their excretion, movements, and burrowing. Ultimately, the cell and its multienzyme system derived from many of its specialized organiods, that dispose of compounds and elements in an orderly fashion. Theoretically, the cell and its macromolecular framework could do their handiwork without the worms and tiny, tiny critters. Heterotrophic and autotrophic activities of bacteria usually take care of most of what we throw in our aquariums rather efficiently.

TTYL Sam