druluv
Member
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. Like Rodney Dangerfield, "They don't get no respect." That is a pity, as 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. I have done sampling to measure the abundances found in the 45 gallon tank I mentioned earlier, and the number of animals larger than half a mm, or about one fiftieth of inch, in that tank ranges from 90,000 to 150,000 depending on what part of their population cycle the various species are in.
Left. An harpacticoid copepod, about 1/50th of an inch long. Barely visible, these small crustaceans are an important part of the food chains and clean-up crews in our tanks. They live on and in the sediments. Center. A group of tube-dwelling bristle worms, probably chaetopterids, in my 60 gallon Stichodactyla tank. These animals are primarily filter feeders catching small particles with their paired feeding tentacles. Left. The head end of a small predatory bristle worm called a syllid. These probably eat other small worms and move through the sediments in search of them. This worm was about 1/10th of an inch long.
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. In my 45 gallon tank, with an average population of about 100,000 small animals, from one to ten million cubic millimeters of sediment is moved each day. Or phrased another way, the entire tank's sediment volume could be completely turned over at least once every three to thirty days. 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...
A baby fire worm found in the sediment bed of my 45 gallon lagoonal reef tank. Juvenile worms such as this are commonly produced by spawning adult worms, and have passed through a relatively long planktonic larval stage in the tank water. Most of the babies perish by being eaten by corals and other suspension feeders.
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.
Construction:
Making a sand bed is almost too easy. The most important part of the sand bed is, not surprisingly, the sand. While earlier I referred to "mud" and now I refer to "sand," I am not discussing two different materials. There is no scientific definition of "mud," however, those of us befuddled folks who spend part of our life working with marine sediments have a naming scale for the parts of the continuum of particles ranging from the very big ("boulders" = particles over 25.6 cm, about 10 inches, diameter) to the very small ("clay" = particles less than 0.004 mm, about 0.00016 inches). Nowhere in this scale is there a mention of that most desirable of substances, "mud." Generally, what a sediment-studying scientist would refer to as fine or very fine sands with smidgen of silt, most normal folks call mud. These are sediments whose particles generally range from about 1/16th mm (0.063mm) to about 1/8th mm (0.125 mm).
What's all the fuss about sediment grain size, anyway?
In all of my discussions about sand beds I have made a point of specifying one particular parameter, that of the average size of sediment particles in the sand bed. Why should this one factor be so important? The answer simply is that sediment particle sizes determine the acceptability of the sediment to the organisms. Perhaps an example might illustrate this statement better. One of the common amphipods found along the west coast of North America is a species called Rhepoxynius abronius. This small bug has been investigated in some detail as an organism to use to test the toxicity of sediments, has been found to prefer sediments of a specific particle size, 0.113 mm in diameter. If given a choice, it will move to and live in sediments of that one specific size, not sediments 0.110 mm nor sediments of 0.115 mm, but only of that one size. If individuals are experimentally confined to other sediment sizes, they neither live as long, nor reproduce as well, nor tolerate stressful conditions as do individuals kept at the optimum grain size (Ott, 1986).
Most sediment-dwelling organisms appear to have similar 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.
A good sediment particle size distribution for a sand bed.
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.
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. Like Rodney Dangerfield, "They don't get no respect." That is a pity, as 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. I have done sampling to measure the abundances found in the 45 gallon tank I mentioned earlier, and the number of animals larger than half a mm, or about one fiftieth of inch, in that tank ranges from 90,000 to 150,000 depending on what part of their population cycle the various species are in.
Left. An harpacticoid copepod, about 1/50th of an inch long. Barely visible, these small crustaceans are an important part of the food chains and clean-up crews in our tanks. They live on and in the sediments. Center. A group of tube-dwelling bristle worms, probably chaetopterids, in my 60 gallon Stichodactyla tank. These animals are primarily filter feeders catching small particles with their paired feeding tentacles. Left. The head end of a small predatory bristle worm called a syllid. These probably eat other small worms and move through the sediments in search of them. This worm was about 1/10th of an inch long.
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. In my 45 gallon tank, with an average population of about 100,000 small animals, from one to ten million cubic millimeters of sediment is moved each day. Or phrased another way, the entire tank's sediment volume could be completely turned over at least once every three to thirty days. 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...
A baby fire worm found in the sediment bed of my 45 gallon lagoonal reef tank. Juvenile worms such as this are commonly produced by spawning adult worms, and have passed through a relatively long planktonic larval stage in the tank water. Most of the babies perish by being eaten by corals and other suspension feeders.
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.
Construction:
Making a sand bed is almost too easy. The most important part of the sand bed is, not surprisingly, the sand. While earlier I referred to "mud" and now I refer to "sand," I am not discussing two different materials. There is no scientific definition of "mud," however, those of us befuddled folks who spend part of our life working with marine sediments have a naming scale for the parts of the continuum of particles ranging from the very big ("boulders" = particles over 25.6 cm, about 10 inches, diameter) to the very small ("clay" = particles less than 0.004 mm, about 0.00016 inches). Nowhere in this scale is there a mention of that most desirable of substances, "mud." Generally, what a sediment-studying scientist would refer to as fine or very fine sands with smidgen of silt, most normal folks call mud. These are sediments whose particles generally range from about 1/16th mm (0.063mm) to about 1/8th mm (0.125 mm).
What's all the fuss about sediment grain size, anyway?
In all of my discussions about sand beds I have made a point of specifying one particular parameter, that of the average size of sediment particles in the sand bed. Why should this one factor be so important? The answer simply is that sediment particle sizes determine the acceptability of the sediment to the organisms. Perhaps an example might illustrate this statement better. One of the common amphipods found along the west coast of North America is a species called Rhepoxynius abronius. This small bug has been investigated in some detail as an organism to use to test the toxicity of sediments, has been found to prefer sediments of a specific particle size, 0.113 mm in diameter. If given a choice, it will move to and live in sediments of that one specific size, not sediments 0.110 mm nor sediments of 0.115 mm, but only of that one size. If individuals are experimentally confined to other sediment sizes, they neither live as long, nor reproduce as well, nor tolerate stressful conditions as do individuals kept at the optimum grain size (Ott, 1986).
Most sediment-dwelling organisms appear to have similar 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.
A good sediment particle size distribution for a sand bed.
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.
