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Sand Bed Systems Sam Gamble Aquarium.Net Feb 97

Sam Gamble continues his series of articles on sand bed systems for reef aquariums, Aquarium Net has numerous articles written by the leading authors for the advanced aquarist

Sand Bed Systems

Sam Gamble

In last month's article the danger of tracking in nuisance algae problems was discussed. The important factor was the organic content of the rocks that we sometimes use. Next, a similar problem occurs with sand used for the sand bed itself. Because we have built the sand bed filter to function a prescribed way, the mechanisms for problems become a little more complex and interrelated. When problems occur it's more than a load of nutrients and a conditioned surface.

In general, the important components of the sand bed are biological mediators, sand type, and grain size. Correctly orchestrating these contributing elements will achieve the balance and equilibrium the system needs. Like rocks, the amount of organic compounds in the sand is a contributing stress factor and will be treated separat

The focus begins at the sand to water interface and diffuses into the bed beneath. With the construction of the plenum space we have effectively produced an environment that is not reliant on the anaerobic condition. In most cases, once sand bed filters are cured, it is hard to find areas in the sand bed with less than 1 mg/l dissolved oxygen.

In general the surface of the sand bed is very active with oxygen demanding heterotrophs. They begin the sequence of reduced compounds, reduced oxygen, and lowered redox. The list of microbes species is long, as is the list of chemical transitions. The important thing is the balance of the consortium.Where you get the inoculating live sand will determine the ratio of organisms. From there, the natural mechanisms proceeed with microbial colonization of the constructed sand bed. The rate of development and the end result will be influenced by what you start with.

The area where the live sand was collected will determine the number and types of microbes it contains. In very general terms, live sand from near shore will be the same as live sand that has its origin from a fore reef area. NOTE THE WORD GENERAL. This will not be good enough to get you off to an advantageous start. Chosing a more specific sampling of microorganisms will start a prof oundly better successional colonization of the virgin bulk sand,that makes up your sand bed. Sand sampled from a successful aquarium will do it. A quality live sand sampled from the top layer of the sandy bottom in a fore reef will also. This is where some cultured sands get their starting stock.

Inadequate sand is deficient in other important components, like sand type. Sand type involves the sand's geological history before you got it. It s understandable that a preferred sand comes from an area resulting from the deposited remains of previous reefs. For example, this doesn't include Virginia Beach.

Hence we have the GEOlogical importance of aragonite sand. When dug up and processed the aragonite sand is basically fossilized reefs, that contain the basic elements to build new reefs, without any recent organic deposits. Most importantly this is usable calcium and all essential trace elements. In our particular case, the new reef being built is in the aquarium. Historically the mechanisms regulating elemental depositing and release, have been governed by natural processes. We have recently learned how to harness these mechanisms, technically and/or naturally.

Processing the sand includes grading the sand for size and uniformity. Size is important because large grain size sand will contain less bacteria than small grain size. It's a function of surface area. The cut off is the size regarded as silt. Whereas silt will have more surface area, it inhibits flow around the sand by diffusion. Silt will have a tendency to collect organic compounds and have little or no oxygen associated with it. Producing an anaerobic environment is not what we want. It's the reduced oxygen or anoxic environment we're looking for.

A sand that has an average grain size of 2 mm has shown to produce the reduced oxygen environment needed for the designed anoxic - passive filtration. Uniform grain size will aid the overall efficiency for this goal. Uniform pore water around the sand grain will help the diffusion of elements to and from the sand bed. It is impossible to produce and maintain a perfectly homogeneous sand bed, but having sand that is relatively uniform to start with is a big plus. The chemical transitions of compounds and elements back and forth from the living cells (microbes) will be greatly enhanced by the ability to move, diffuse.

Diffusion is a very good process over short distances. With our sand bed filtration we are counting on it. To limit it in some way, we are effectively reducing the capability to metabolize and cycle organic material and the elemental by-products. In simplest terms, this is CHEMICAL transformation and interaction.

Putting together some of these general concepts, we have BIOlogy, GEOlogy. and CHEMICAL pathways for the mechanisms of the sand bed filtration. Does "biogeochemical pathways" ring a bell from the first article? When we neglect the components of good sand, then some of the functionality of the filtering capacity is sacrificed. When that happens compounds like "nutrients" end up in the undesirable places and accumulate. What happens with strong light and an abundance of nutrients? Killer algae! This is an example of organic content being produced by imbalance. It can also originate from sand laden with organic compounds.

At the beginning of the article I mentioned organic load can be present in starter sand. Sand from near shore or grassy areas can have high organic content and undesirable microbial situations. Reefs are reputed as being nutrient poor environments where the likelihood of having a sand with reduced organic content is favored. Near shore and estuaries, this is not the case. If you add live sand with a poor selection of microbes, that is packed with nutrients, what would you expect to get? Killer algae!

Going to all the time and trouble to build and stock a new aquarium, but use the wrong sand, you've shot yourself in the foot. Or perhaps, you've tried to follow all the guidelines, and still have algae or incomplete filtration, e.g. nitrate above 20 mg/l, what then? It's time for remedy and treatment, Rx and Tx. You'll need some water quality information to base Rx & Tx. It's basically an evaluation of where to place the emphasis; bio, geo, or chemical problems.

If algae problems start to occur but the pH, alkalinity, and nitrogen compounds look acceptable, then the situation may stem from nutrients like phosphate being present on the substrate surface. Rx, most often is the laborious task of removing the algae by hand. Sometimes the addition of snails and crabs will help control it, but they are redistributing the nutrients essentially. When the nuisance algae is in response to a high nutrient content of the sand, then off loading the problem is quicker. When combined with natural predators it becomes a little more effective. However, it will not be a quick process. You'll have weeks and perhaps months to work with the problem. Tx, chemical additives to absorb nutrients, only work on the compounds dissolved in the water that pass through the media. Phosphate has a tendency to coat surfaces, so it won't be effected too much. One of the reasons removing the algae by hand is effective. All that has gone into the algae to build it, is removed with the algae. Nature packages it, and you do the shipping on a oneway ride.

If your water quality starts off within an acceptable range, but begins to deteriorate, e.g. pH drops below 8.2, and nitrate gradually increases, then the problem may stem from microbial problems. If the microbes responsible for filtration and cycling are not growing and functioning, the water quality starts to accumulate nutrients. Rx and Tx, basically have two routes, to remove the bad water (water exchanges) or RX, give the microbial populations help, reinforcements.

Water changes are merely diluting the problem until the filtering and cycling work force can catch up to the load presented to it. The microbes are more essential to maintain. I have used a couple of good ways to succeed in this task. One is to accelerate the reaction rate of the microbial cells. This is done simply by adding the correct spectrum of biological enzymatic catalysts. The other is to add more microbes.

Adding more microbes can be done by adding more live sand. But, if the live sand is the same that resulted in the problem in the first place, not much is gained. Would recommend a new source of live sand. Try to get sand that comes from a reef environment, another well functioning aquarium, or a well reputed cultured sand.

It stands to reason, if you add a better quality live sand and give it a boost with catalysts, you are promoting a lasting change. The biological and chemical pathways just got a shot in the arm to increase natural capabilities. An ecosystem to remain healthy must continually change and try to achieve balance., and not just remove nutrients.

In this method you are not subtracting anything. You are providing more natural tools and mechanisms to cycle components to usable form, or dispose of them through the pathways inherent to equilibria. Metabolism occurs in an appropriate proportion to the conditions given. That's the crux of many problems; " to the conditions given".

Much of the emphasis on sand bed filtration is the treatment of nitrate as described by natural nitrate reduction. All aquariums have natural nitrate reduction to some extent. It can occur in any sand bottom, rocks, hidden detritus, biofilms, algal mats, micro algae, macro algae, and etc. In some cases it is reducing the NO3 molecule to its elements. In others, it is assimilated to new compounds like NH3.

Without the synergy of a balanced sand bed, you are not getting some of the natural sources and sinks for biogeochemical processes that are mediated by microbial organisms. Most of which are single cells living in colonies. They are naturally selected for the metabolisms that the nitrogen cycle is only a concomitant part of. The ecology of the sand bed is also responsible for self regulating carbon sources, a natural and self regulating buffering capacity, resident sulfur reduction and regeneration, steady source of trace elements, energy flux, and a natural tendency to promote equilibria during stress.

To get this industrious natural package, you have to use good ingredients. Just a bucket of "live sand" may not do it. Read the label and check the ingredients, so to speak. Your sand needs to be environmentally friendly for your new aquarium. It needs the correct BIOlogical representatives, in the correct GEOlogical conditions, carrying out essential CHEMICAL transitions to obtain anything that resembles equilibria of a substrate oriented natural filter.

This illustrates several of the common situations with substrates. Next time some of the negative situations that animals cause will be illustrated. How many reef keepers have gone to their favorite aquarium store looking for a large, healthy mantis shrimp?

Created by liquid
Last modified 2006-11-18 18:31