And this says it ALL.
If this doesnt open minds and TEACH something, Nothing will.
FROM REEF-AQUARIUM...
The Importance of a Deep Sand Bed
The most important component of a coral reef aquarium is a deep sand bed, comprised of very fine sandy sediments.
Benefits
Most coral reefs are surrounded by sand area and by constructing a sand bed in our aquariums we merely emulate nature. These beds provide three things. First, they provide a place for processing and exporting some dissolved nutrients. Second, they provide a place to recycle detritus, excess foods, animal feces and other particulate material into useable forms. Finally, they provide a food source for many reef animals. Let's look at each of these functions.
As they do in nature, the sand grain surfaces of sand beds in our systems provide the major substrate for nutrient processing bacteria. The bacterial population is determined by three factors: the total sand surface area; the amount of nutrient available; and the number and effects of bacterial predators. All of these play a role in the development of the sand bed biological filter.
In a given volume of sand, the usable bacterial surface area rises rapidly as the average particle size decreases. The total sediment surface area in even a small tank is impressive, indeed. In a 45 gallon reef tank where the sand bed averages about 4 inches deep, by 12 inches wide, by 36 inches long, for a total of one cubic ft of sediment. If the average particle size is one eighth mm, and that is a good average size to have, the total sand surface area is about 14,828 square feet or just slightly over 1/3 of an acre. A LOT of bacteria can live with that amount of space! The surface area for bacteria and microalgae in live rock or on other surfaces is insignificant compared to the area in a sand bed four or more inches in depth.
Although we seldom consider bacteria when we set up our systems, they are exceptionally important to the survival of every decorative fish or coral we add to the tank. Those bacteria are the biological filter of your reef tank, and by their simple existence and growth they detoxify and remove many of the excess nutrients from the system.
One organism's poison is another's nutrient. Fish and invertebrate urine, largely ammonium hydroxide, or ammonia gas dissolved in water, is the primary byproduct of necessary protein metabolism. Ammonia gas, even very small amounts dissolved in water, is highly toxic to animals. Likewise, phosphates are also byproducts of animal metabolism, and although not toxic to most animals, high phosphate concentrations reduce or stop coral growth. The removal of both nitrogenous wastes, such as ammonia, and phosphates is accomplished by bacteria and microalgae which absorb these toxic animal byproducts and use them in their growth as necessary, required, and vital nutrients.
The cardinal rule of animal husbandry is that you have to feed animals, and many reef animals need to eat a lot. Simply feeding your fish or corals the necessary food they need to live may boost ammonia and phosphate concentrations several hundred to several thousand times what is normally found in reef water. But, if you have a deep sand bed, a process that is nothing short of miraculous occurs. The bacteria and algae living in the sediments take up the nutrients so fast and so thoroughly, that hobbyist test kits typically may not measure any of the nutrients at all even immediately after feeding.
These nutrients act as food for the bacteria. In a very real sense, the biological filter depends upon bacterial growth. The breakdown of nitrogen compounds to nitrogen gas is done by bacteria growing in the areas of lowered oxygen concentration in the deeper parts of the sediments. At normal reef temperatures, around 82 deg F, some bacterial species will double their population in less than a half hour if they have the appropriate nutrients. This rapid bacterial growth rate causes the release of nitrogen gas which becomes visible as bubbles in the sediments.
Rapid bacterial growth rates only occur without competition for space or nutrients. As the bacterial populations fill in all the open spaces growth slows and may stop altogether. Some bacteria also secrete a exterior covering called a glycocalyx. These are made of a hard sugar-like material similar in consistency to rock candy. Rapid bacterial growth may produce so enough of this material to glue sediments together. These sediment lumps may be glued so tightly together that hammering is needed to break them apart.
Lump formation is a disaster for the biological filter. The lumps restrict water flow and trap organic material where it can rot. Additionally, lump formation shuts down the biological filter by covering the bacteria and preventing them from metabolizing nutrients. This, in turn, causes the tank nutrient levels to skyrocket.
Fortunately, prevention of sediment clumping and the simultaneous maintenance of optimal biological filter operation is easily done by the establishment of a healthy and diverse sediment dwelling fauna, or "infauna." The infauna, so-called as the FAUNA lives IN the sediments, is a very diverse array group of wonder-working organisms. Unfortunately, they are small, and are not particularly attractive. But they do most of the work in keeping any reef tank functional.
The infauna are "the clean-up crew" and the "reef-janitorial" staff, and the array found in a successful tank may be DIVERSE! More than 200 different species commonly are found living in a mature sand bed. These include many types of flatworms, round worms, dozens of species of bristle worms, small snails, brittle stars, small sea cucumbers, protozoans, and many types of small crustaceans. The total populations may be immense.
What does this diverse and abundant array of critters do for and in the sand bed? Well, some will eat excess food, detritus, or algae. In doing so, they utilize it, and excrete part of it as waste. In turn, bacteria utilize that, and thus the infauna help keep the biological filter going. Additionally, many infaunal animals burrow ingesting some sediments as they go. They digest the microorganisms off of them, opening space for bacteria to grow.
By moving through sediments, the animals jostle and move the particles. Not much, just a little tiny bit. It has been estimated that each day each small organism moves about 10 to 100 cubic millimeter of sediment. Multiplying this tiny average amount of jostling by the number of animals in the tank gives the total amount of disturbance. With this amount of jostling and sediment eating, sediment clumping the sediments will simply not occur.
Consequently, excess food is eaten and disposed of or recycled as animal or algal flesh, and that the biological filter is maintained in the best of condition. And, best of all you, as the aquarist, didn't have to do anything. The animals did it all for you. All you had to do was to sit back, and enjoy a healthy tank. And, yes, I know it was a dirty job, but somebody had to do it....
But this isn't all the good a sand bed will do for your system! Most of the infauna live a year or less. However, they grow rapidly and start reproducing within a few weeks after they were spawned. Cumulatively, they produce large amounts of small eggs, sperm, and larvae that are liberated invisibly into the tank's water. All the spawned material has the potential of becoming food for many small-polyped stony corals as well other filter feeders. It is no coincidence that, historically, aquarists began to be able to keep many of these small polyped corals when they started keeping a sand bed in the aquarium for the first time.
What's all the fuss about sediment grain size, anyway? The answer simply is that sediment particle sizes determine the acceptability of the sediment to the organisms. Most sediment-dwelling organisms appear to have precise preferences. However, most will also live at least marginally well in mixed-sediments with sizes around their optima, and most sediment particle size optima seem to be in the range of 0.050 to 0.200. Consequently I suggest a range averaging about 0.125 as a good compromise. It isn't specifically the best for most infaunal species, but it will allow a diversity of species to live pretty well.
Coarser sediments such as gravel or crushed coral are simply too big. Additionally, they have the drawback of being sharp edges that are abrasive to many of the small crustaceans and worms that must crawl through the sediments. Finer sediments can pack so tightly together that they are impervious to most animal movement, creating a layer that restricts animal and water flow shutting down the biological filter.
Having to assess sands for particle sizes would be a daunting task for any hobbyist. Fortunately, however, several vendors sell bulk sands in the appropriate size ranges, often marketed as "sugar fine" or oolitic sands. A few larger particles in the sediment mix is okay, but larger sediments should not constitute more than about 15 percent of the total. Under NO circumstances should you use crushed coral or coral gravel. These substrates are too coarse and often too abrasive for many of the smaller organisms to survive in.
Additionally, there are several vendors offering "detritivore" or "recharge" kits having several different types of animals in them. Kits from different vendors are complementary rather than competitive. Adding one kit is good, adding two is really better. You will get a more diverse system faster with more kits. However, their cost may be prohibitive. Once the kits are in, let the system go for at least two weeks without adding fish to allow the live sand animals to establish minimal populations. Remember these are living animals, and will need to be fed.
Within a week, you should notice bubbles in the sediment next to the glass indicating the sand filter is working, within a couple weeks small tube traces should be visible in places in the sediments near the walls, and small bug populations should be evident. UNDER NO CIRCUMSTANCES SHOULD YOU ADD "SAND-SIFTING" ANIMALS SUCH AS BURROWING SEA STARS OR SOME GOBIES. These animals are "sifting" the sediment to eat the sand critters that you need to have thrive.
Problems
More imagined than real problems bedevil keepers of sand beds. The imagined problems are proposed by people who are ignorant of the sand bed dynamics. Among these imaginary problems are accumulations of hydrogen sulfide and detritus, and the need for sifting. Hydrogen sulfide will indeed be formed in the lowermost layers of a deep sand bed. It will NOT migrate up through the sediments to poison a tank. Hydrogen sulfide is an amazingly toxic gas, but that toxicity is exceeded by its pungent rotten-egg odor. The gas will have an exceptionally strong odor, and will seem overwhelming at levels well BELOW toxic amounts. If you can smell this stuff without it literally taking your breath away, it won't be at a harmful concentration. There is no real evidence to indicate that it may reach toxic levels in a deep sand bed.
Detritus build up in the sediment is another non-problem. If the sediment fauna is thriving, there will be a slight build up of fine detritus while the rest will be processed by the infauna. The final imaginary problem, the presumed need for sifting in a healthy sand bed, simply does not exist. Small organism movements "sift" the sand sufficiently. Any other sifting of a healthy bed will cause serious harm.
Sand beds recycle materials and export many of the excess nutrients in an aquarium. Some excess nutrients are mobilized by becoming soluble through metabolic processes and need to be exported either as harvestable macroalgae or animals, grown in the main tank or a sump.
The only real problem with a sand bed is the reduction in diversity as the bed ages. This is caused by extinction and replacement problems because the volume of our beds is simply too small for some species to generate self-sustaining populations. This is remedied, by purchasing a detritivore or recharge kit or two every year or so to give a boost to the fauna.
Conclusion
The installation of a live sand bed is easy, straight-forward, and inexpensive relative to almost all other aquarium purchases. Once established, such a bed will contribute much to the success of a reef tank by providing a biological filter with sufficient capacity to for most tanks. Additionally it will provide food for many of the suspension feeding animals such as small polyped stony corals. And, it will do this all with a minimum of care and expense.
