What is biological filtration?
Biological filtration is the use of beneficial bacteria to eliminate organic waste compounds from a body of water. It is distinguished from mechanical filtration, which is a process whereby water is strained and suspended material is physically removed from the water. The bacteria that do the work in a biological filter are part of the "nitrogen cycle," a series of events that also occurs in nature.
Why is it important?
By eliminating the organic waste compounds in the water, biological filtration detoxifies the water and makes it safe for fish. Additionally, by removing the organic waste compounds, algae is controlled because those compounds are the nutriment that algae require in order to grow.
What is a biological filter?
A biological filter or "bio filter" is simply a home for the beneficial bacteria that perform the nitrogen cycle. The filter provides surface area that the bacteria can live on and a recirculating water pump ensures that water is constantly flushing over the bacteria so they can obtain their necessary nutriment and oxygen.
Where do the Bacteria come from?
The bacteria occur naturally in a pond. They live on fish and other underwater surfaces such as plant stems and rocks. In order to get the bacteria established in a filter or new environment, aquarium and pond owners used to borrow some gravel that had bacteria on it from an existing system. This cumbersome procedure is no longer necessary as there are now available bottled viable bacteria cultures in either living form or freeze dried spores.
If the bacteria occur naturally, why is a bio filter necessary?
Most backyard ponds have a much higher concentration of fish than would occur in nature, and the fish are usually fed a high-protein food. These facts result in a higher concentration of organic waste, i.e., ammonia,than the naturally occurring bacteria can deal with. A bio filter houses more bacteria, hopefully enough bacteria, so that ammonia and the other nitrogen compounds are completely eliminated.
Why do ponds turn green?
Ammonia is at the root of most green water (algae) problems. As discussed below, ammonia forms naturally in the pond and is toxic to fish. Ammonia may be eliminated by the beneficial bacteria in a properly operating bio filter, but if it is not, the pond could become toxic were it not for algae. Algae is nature's safety net for fish. If ammonia levels rise, algae will colonize the pond and make it safe for fish by taking up the ammonia as nutriment.
The Nitrogen Cycle
The nitrogen cycle consists of three basic steps; 1) ammonia to nitrite, 2) nitrite to nitrate, 3) nitrate to free nitrogen. Ammonia is created from two sources- fish and other animal waste, and decaying organic debris (leaf litter, pollen, etc.) that gets into the pond. To complicate matters, ammonia is present in two forms - free (NH3) which is very toxic to fish, and ionized(NH4-) which is still toxic but less so. The higher the pH, the greater the ratio of the more toxic free form to the ionized form. Nitrosomonas bacteria oxidize ammonia into nitrite by the addition of oxygen, and nitrobacter bacteria oxidize nitrite into nitrate. These two types of bacteria are referred to as "nitrifying bacteria," and live on surfaces in the pond, such as plant stems, rocks and even on the fish themselves. They require oxygen in order to live and to perform their function.
Nitrate is eliminated by "denitrifying bacteria" that live in the bottom mud. These mud dwellers are anaerobic bacteria that die in the presence of oxygen, and, as they do their work converting nitrate to free nitrogen, also release hydrogen sulfide and methane gases - the swamp smell. Most clean, well aerated backyard ponds do not have an anaerobic environment or chamber, and nitrate thus accumulates in the pond. It is nowhere near as toxic to fish as are ammonia and nitrite, but it is a nitrogen fertilizer and will encourage an algae bloom. Fortunately for beleaguered pond owners, there are now available proprietary formulations of bacteria that eliminate nitrate in the presence of oxygen. These bacteria can be added to the pond and thus allow the nitrogen cycle to be completed so that algae will not colonize the pond. Otherwise, plants, periodic partial water changes or algae must be relied upon to remove the nitrate.
Two types of biological filters
There are two basic types of bio filters; in-pond and out-of-pond. Out-of-pond filters are further divided into two types - pressurized and non-pressurized. In-pond filters are typically used in smaller ponds, say up to about 1500 gallons, and out-of-pond filters are typically used in larger ponds, although this rule is far from absolute. The main function of any type of bio filter (i.e. providing a home to bacteria ), is the same regardless of design. The differences are in cleaning, space requirements, and add-on enhancements.
An in-pond filter has a submersible pump attached, and all the equipment is in the pond. The advantages are ease of installation and cost economy. The disadvantage is that you have to reach into the pond to clean the filter. Some in-pond filters have only a sponge for the bacteria to live on and do not work very well because the bacteria are killed off every time the sponge is cleaned. Others, such as the Bio+Plus, have separate mechanical and biological chambers, and are much more efficient.
Out-of-pond non-pressurized systems are the oldest form of bio filter - a simple gravel bed. Usually the water is pumped into the filter below the gravel, with a gravity flow back to the pond, although with proper engineering the reverse can also be set up. Gravel bed filters are custom built at the pond site and are very difficult to clean unless expertly engineered.
Out-of-pond pressurized filters
Out-of-pond pressurized filters are typically swimming pool sand filters that are modified for pond use. (Diatomaceous earth and cartridge type swimming pool filters are generally not used in ponds, as they get clogged up too fast.) These filters have the advantage of being very easy to clean and, because the water is under pressure, are very flexible for variations installation requirements. A problem for the inexperienced installer is that all the instructions that come with these types of filters are for spas or swimming pools - not for ponds. Sizing of pump, canister, and medium are different for ponds, and only the side-mounted multiport valves provide a sufficient backwash. When they are sized and maintained properly, they provide excellent bio filtration.
What makes a pressurized filter so easy to maintain is the multiport valve that controls the flow of water through the filter. There are backwash and rinse positions that allow pond water to be used to clean the filter. The dirty water is discharged to waste, and the whole process only takes a minute or so. If the sand grain size is too small, however, back-washing will not be effective, and water will channelize through the filter, greatly reducing efficiency.
Set up and Maintenance
Since the primary purpose of a bio filter is to provide surface area for beneficial bacteria to live on, the size of the filter depends upon the amount of organic waste the bacteria have to deal with. The amount of waste is a function of the fish population, debris that blows in from nearby plants and trees and water plants such as water lilies that drop a lot of debris of their own. There's not much reason to have an over-sized bio filter,as the bacteria population will only be as large as the organic waste warrants. The exception to this rule is a poorly designed or hard-to-maintain filter that is inefficient and requires a larger surface area because the bacteria are struggling to survive.
In-pond-filter
The filter should be placed as far away from a waterfall or fountain as is practical. If the pond is deep, it may be set on blocks for easy access and cleaning. Typically, tubing runs from the discharge of the submersible pump that is attached to the filter to a waterfall or fountain. The water then circulates through the full range of the pond, and stagnant areas are avoided. If there is no waterfall or fountain, a venturi T should be added to the discharge tubing to ensure proper aeration.
Out-of-pond pressurized filter
Water is drawn from the pond, through the pump to the filter and then back to the pond. Typically a non-submersible pump is used that has sufficient power for proper back-washing. The water may be drawn from the pond through a surface skimmer, which helps considerably in maintaining good water quality.
PVC pipe, usually 1 1/2" or 2.0" depending on pipe length and pump size, is trenched from the pond to the pump, which is normally located next to the filter but need not be. However, since the pump must be shut off everytime the position of the multiport valve is changed, the on/off switch should be near the filter. There two discharge pipes from the filter; return-to-pond, and waste. The return-to-pond pipe may be T'd and valved so that water may return via the waterfall or through an underwater jet.
Fluidized-Bed Filters
Fluidized-bed filters are a very unique biological filter. If properly designed and built tall enough, they have the ability to cultivate not only aerobic nitrifying bacteria, but also facultative anaerobic denitrifying bacteria. This means they may have the capability to remove not only ammonia and nitrite, but also nitrates. They usually consist of some type of column chamber which houses several cups or more of coarse sand or similar media. Water enters at the bottom of the filter and exits at the top. There is usually a control valve for regulating water flow. A check valve is usually placed on the filter intake to prevent the sand from packing-down when the filter is turned off.
Because water flows upward through the filter, the sand in the filter becomes suspended or "fluidized" in the water column, forming a fluidized bed of sand. If the flow of water is controlled properly, the sand does not flow out of the filter, but remains suspended. This happens because the flow of water is just fast enough to keep the sand in suspension. The weight of the sand prevents it from escaping the filter. Because the sand is suspended in water, fluidized-bed filters are self cleaning, and require little or no maintenance.
The water at the bottom of the filter is fresh and high in dissolved oxygen, so aerobic bacteria cultivate in the bottom half of the sand bed, and remove ammonia and nitrite, using up oxygen in the process. In taller fluidized-bed filters, enough aerobic bacteria cultivate in the bottom half so that as water flows past them, they remove most of the oxygen from the water, so facultative anaerobic bacteria cultivate in the top half of the sand bed where they remove nitrates. Not all fluidized-bed filters are tall enough to promote anaerobic denitrifying bacteria, but most are very efficient at cultivating beneficial aerobic bacteria.
Some fluidized-bed filter designs are stand-alone units that are too tall to be placed under an aquarium in a cabinet stand. These are actually the best designs, but are not practical for most aquariums. Other fluidized-bed filters are designed to hang on the back of an aquarium or sit in a reservoir, and may be driven by a small pump or the return line of a canister filter. These types of fluidized-bed filters are an excellent way to provide biological filtration on an aquarium equipped only with a canister filter.
Plenum Systems
Describing a plenum requires far more than just a single paragraph. The plenum method was discovered by Dr. Jean Jaubert and is often referred to as the Jaubert System. "Plenum" refers to an un-oxygenated layer of water trapped beneath a deep layer of gravel or sand at the bottom of an aquarium. This layer of water becomes anaerobic. Bacteria cultivate in this oxygen-free environment and remove nitrates from the aquarium. There are several variations of the plenum, depending on what literature you read.
The basic structure of the plenum system is essentially a deep (3" to 4") layer of gravel, suspended 1/2" to 1" above the bottom of an aquarium. It is usually recommended that very little or no water flow should be directed across the gravel surface. A basic plenum may be created by suspending egg crate material or under gravel filter plates above the aquarium bottom, using inert supports such as PVC pipe. If egg crate is used, it is covered with nylon screening over which the deep gravel bed is placed. The actual materials, including what grade of gravel or sand is used, vary depending on what literature you read, but usually coarse live sand, fine coral gravel, or a combination of both are used. One technique is to use 2" of live sand on the bottom, over which nylon screening is placed. The screen is then covered by 2" of fine coral gravel. This allows the aquarist to turn over the top inch of gravel occasionally to clean it, without disturbing the anaerobic layer below.
Anaerobic bacteria form in the bottom depths of the substrate and in the water below. As anaerobic bacteria cultivate, they remove nitrates. Anaerobic action produces a fair amount of heat. The heat warms the water layer below the gravel. The warmer water flows upwards, displacing cooler water above the gravel. This action moves water through the plenum at very slow rates. The slow movement of water through the gravel helps to prevent dangerous hydrogen-sulfide gases from forming in the plenum. The deep gravel bed also provides a home for burrowing motile invertebrates which feed on solid organic mulm and detritus. These burrowing animals, which are either purchased and/or cultivate on their own from live rock, serve to keep the plenum porous and aid in the slow movement of water through the system. "Burrowing" sea cucumbers that serve this function well may be purchased from a good aquarium store.
The aquarium is stocked with live rock, but not as much as is typically used. The live rock construct should be suspended above the gravel bed, allowing water to move freely beneath the reef. This may be accomplished in a number of ways. One way is to place a couple of "anchor" pieces on the gravel bed, and glue others to the back of the tank using aquarium epoxy putty (not silicone!). The rest of the live rock may then be bridged across these supports to build the reef, but not too high. The construct should be loose, not tightly packed together, to allow good flow through the rock. Care should be taken not to direct flow from pump returns across the gravel. The emphasis in aquariums using a plenum should be on the reef, with a minimal number of fish to balance the ecology.
The Jaubert Plenum System, if constructed properly, can work well, provided the aquarium is only lightly-stocked with fish. While we are sure some hobbyists would disagree with us here, we feel that more research is necessary on this fascinating subject. The original plenum method used aeration as the only means of water movement in the tank. We highly recommend that a plenum be used in conjunction with a Berlin system. The protein skimmer will remove other dissolved and solid organics, not removed by the plenum. The use of a protein skimmer combined with the plenum method may be the key to keeping more fish while using this type of biological filtration. If you're setting up a new aquarium, installing a plenum will be relatively easy. If you have an existing reef tank, installing a plenum will involve a fair to major amount of work. Definitely read up on the subject before you go to work.
Pumps
The rule of thumb is to pump the volume of the pond through the filter once an hour, with a higher turnover rate for small ponds (say, under 500 gallons) and a lower rate okay for larger ponds (say, over 2500 gallons). The pump must operate 24 hours a day in order to keep the bacteria alive. It is much better to have a smaller pump that is cheaper to operate running all the time than to have a larger pump that is shut off part of the day.
Sometimes a two-speed pump makes a lot of sense. It runs on low all the time to save energy costs and on high for back-washing or when a major water flow is desired. The new electromagnetic submersible pumps draw about one-seventh the energy of that of a similarly sized conventional pump, but they are limited in size.
What can go wrong?
If the bacteria colony is not thriving, ammonia will accumulate and algae will colonize the pond. The most common problems with bio filters (beyond poor design) are shutting off the pump for part of the day, improper cleaning, chlorine or chloramine in the water supply and copper leaching into the water from copper pipes. As previously noted, the pump must operate 24 hours a day. If the water source has chlorine or chloramine added, it can not be used to clean the filter as it will kill the bacteria. Furthermore, a chemical detoxifier must be added to the pond in an amount sufficient to treat new water added for topping up. If copper is present, it too must be detoxified with a proprietary water conditioner.
Both nitrifying and denitrifying bacteria should be added on a regular basis.
The sand in a pressurized filter should be checked after backwashing to ensure that it is clean. If not, a larger grain may be required.
Biological filtration is the use of beneficial bacteria to eliminate organic waste compounds from a body of water. It is distinguished from mechanical filtration, which is a process whereby water is strained and suspended material is physically removed from the water. The bacteria that do the work in a biological filter are part of the "nitrogen cycle," a series of events that also occurs in nature.
Why is it important?
By eliminating the organic waste compounds in the water, biological filtration detoxifies the water and makes it safe for fish. Additionally, by removing the organic waste compounds, algae is controlled because those compounds are the nutriment that algae require in order to grow.
What is a biological filter?
A biological filter or "bio filter" is simply a home for the beneficial bacteria that perform the nitrogen cycle. The filter provides surface area that the bacteria can live on and a recirculating water pump ensures that water is constantly flushing over the bacteria so they can obtain their necessary nutriment and oxygen.
Where do the Bacteria come from?
The bacteria occur naturally in a pond. They live on fish and other underwater surfaces such as plant stems and rocks. In order to get the bacteria established in a filter or new environment, aquarium and pond owners used to borrow some gravel that had bacteria on it from an existing system. This cumbersome procedure is no longer necessary as there are now available bottled viable bacteria cultures in either living form or freeze dried spores.
If the bacteria occur naturally, why is a bio filter necessary?
Most backyard ponds have a much higher concentration of fish than would occur in nature, and the fish are usually fed a high-protein food. These facts result in a higher concentration of organic waste, i.e., ammonia,than the naturally occurring bacteria can deal with. A bio filter houses more bacteria, hopefully enough bacteria, so that ammonia and the other nitrogen compounds are completely eliminated.
Why do ponds turn green?
Ammonia is at the root of most green water (algae) problems. As discussed below, ammonia forms naturally in the pond and is toxic to fish. Ammonia may be eliminated by the beneficial bacteria in a properly operating bio filter, but if it is not, the pond could become toxic were it not for algae. Algae is nature's safety net for fish. If ammonia levels rise, algae will colonize the pond and make it safe for fish by taking up the ammonia as nutriment.
The Nitrogen Cycle
The nitrogen cycle consists of three basic steps; 1) ammonia to nitrite, 2) nitrite to nitrate, 3) nitrate to free nitrogen. Ammonia is created from two sources- fish and other animal waste, and decaying organic debris (leaf litter, pollen, etc.) that gets into the pond. To complicate matters, ammonia is present in two forms - free (NH3) which is very toxic to fish, and ionized(NH4-) which is still toxic but less so. The higher the pH, the greater the ratio of the more toxic free form to the ionized form. Nitrosomonas bacteria oxidize ammonia into nitrite by the addition of oxygen, and nitrobacter bacteria oxidize nitrite into nitrate. These two types of bacteria are referred to as "nitrifying bacteria," and live on surfaces in the pond, such as plant stems, rocks and even on the fish themselves. They require oxygen in order to live and to perform their function.
Nitrate is eliminated by "denitrifying bacteria" that live in the bottom mud. These mud dwellers are anaerobic bacteria that die in the presence of oxygen, and, as they do their work converting nitrate to free nitrogen, also release hydrogen sulfide and methane gases - the swamp smell. Most clean, well aerated backyard ponds do not have an anaerobic environment or chamber, and nitrate thus accumulates in the pond. It is nowhere near as toxic to fish as are ammonia and nitrite, but it is a nitrogen fertilizer and will encourage an algae bloom. Fortunately for beleaguered pond owners, there are now available proprietary formulations of bacteria that eliminate nitrate in the presence of oxygen. These bacteria can be added to the pond and thus allow the nitrogen cycle to be completed so that algae will not colonize the pond. Otherwise, plants, periodic partial water changes or algae must be relied upon to remove the nitrate.
Two types of biological filters
There are two basic types of bio filters; in-pond and out-of-pond. Out-of-pond filters are further divided into two types - pressurized and non-pressurized. In-pond filters are typically used in smaller ponds, say up to about 1500 gallons, and out-of-pond filters are typically used in larger ponds, although this rule is far from absolute. The main function of any type of bio filter (i.e. providing a home to bacteria ), is the same regardless of design. The differences are in cleaning, space requirements, and add-on enhancements.
An in-pond filter has a submersible pump attached, and all the equipment is in the pond. The advantages are ease of installation and cost economy. The disadvantage is that you have to reach into the pond to clean the filter. Some in-pond filters have only a sponge for the bacteria to live on and do not work very well because the bacteria are killed off every time the sponge is cleaned. Others, such as the Bio+Plus, have separate mechanical and biological chambers, and are much more efficient.
Out-of-pond non-pressurized systems are the oldest form of bio filter - a simple gravel bed. Usually the water is pumped into the filter below the gravel, with a gravity flow back to the pond, although with proper engineering the reverse can also be set up. Gravel bed filters are custom built at the pond site and are very difficult to clean unless expertly engineered.
Out-of-pond pressurized filters
Out-of-pond pressurized filters are typically swimming pool sand filters that are modified for pond use. (Diatomaceous earth and cartridge type swimming pool filters are generally not used in ponds, as they get clogged up too fast.) These filters have the advantage of being very easy to clean and, because the water is under pressure, are very flexible for variations installation requirements. A problem for the inexperienced installer is that all the instructions that come with these types of filters are for spas or swimming pools - not for ponds. Sizing of pump, canister, and medium are different for ponds, and only the side-mounted multiport valves provide a sufficient backwash. When they are sized and maintained properly, they provide excellent bio filtration.
What makes a pressurized filter so easy to maintain is the multiport valve that controls the flow of water through the filter. There are backwash and rinse positions that allow pond water to be used to clean the filter. The dirty water is discharged to waste, and the whole process only takes a minute or so. If the sand grain size is too small, however, back-washing will not be effective, and water will channelize through the filter, greatly reducing efficiency.
Set up and Maintenance
Since the primary purpose of a bio filter is to provide surface area for beneficial bacteria to live on, the size of the filter depends upon the amount of organic waste the bacteria have to deal with. The amount of waste is a function of the fish population, debris that blows in from nearby plants and trees and water plants such as water lilies that drop a lot of debris of their own. There's not much reason to have an over-sized bio filter,as the bacteria population will only be as large as the organic waste warrants. The exception to this rule is a poorly designed or hard-to-maintain filter that is inefficient and requires a larger surface area because the bacteria are struggling to survive.
In-pond-filter
The filter should be placed as far away from a waterfall or fountain as is practical. If the pond is deep, it may be set on blocks for easy access and cleaning. Typically, tubing runs from the discharge of the submersible pump that is attached to the filter to a waterfall or fountain. The water then circulates through the full range of the pond, and stagnant areas are avoided. If there is no waterfall or fountain, a venturi T should be added to the discharge tubing to ensure proper aeration.
Out-of-pond pressurized filter
Water is drawn from the pond, through the pump to the filter and then back to the pond. Typically a non-submersible pump is used that has sufficient power for proper back-washing. The water may be drawn from the pond through a surface skimmer, which helps considerably in maintaining good water quality.
PVC pipe, usually 1 1/2" or 2.0" depending on pipe length and pump size, is trenched from the pond to the pump, which is normally located next to the filter but need not be. However, since the pump must be shut off everytime the position of the multiport valve is changed, the on/off switch should be near the filter. There two discharge pipes from the filter; return-to-pond, and waste. The return-to-pond pipe may be T'd and valved so that water may return via the waterfall or through an underwater jet.
Fluidized-Bed Filters
Fluidized-bed filters are a very unique biological filter. If properly designed and built tall enough, they have the ability to cultivate not only aerobic nitrifying bacteria, but also facultative anaerobic denitrifying bacteria. This means they may have the capability to remove not only ammonia and nitrite, but also nitrates. They usually consist of some type of column chamber which houses several cups or more of coarse sand or similar media. Water enters at the bottom of the filter and exits at the top. There is usually a control valve for regulating water flow. A check valve is usually placed on the filter intake to prevent the sand from packing-down when the filter is turned off.
Because water flows upward through the filter, the sand in the filter becomes suspended or "fluidized" in the water column, forming a fluidized bed of sand. If the flow of water is controlled properly, the sand does not flow out of the filter, but remains suspended. This happens because the flow of water is just fast enough to keep the sand in suspension. The weight of the sand prevents it from escaping the filter. Because the sand is suspended in water, fluidized-bed filters are self cleaning, and require little or no maintenance.
The water at the bottom of the filter is fresh and high in dissolved oxygen, so aerobic bacteria cultivate in the bottom half of the sand bed, and remove ammonia and nitrite, using up oxygen in the process. In taller fluidized-bed filters, enough aerobic bacteria cultivate in the bottom half so that as water flows past them, they remove most of the oxygen from the water, so facultative anaerobic bacteria cultivate in the top half of the sand bed where they remove nitrates. Not all fluidized-bed filters are tall enough to promote anaerobic denitrifying bacteria, but most are very efficient at cultivating beneficial aerobic bacteria.
Some fluidized-bed filter designs are stand-alone units that are too tall to be placed under an aquarium in a cabinet stand. These are actually the best designs, but are not practical for most aquariums. Other fluidized-bed filters are designed to hang on the back of an aquarium or sit in a reservoir, and may be driven by a small pump or the return line of a canister filter. These types of fluidized-bed filters are an excellent way to provide biological filtration on an aquarium equipped only with a canister filter.
Plenum Systems
Describing a plenum requires far more than just a single paragraph. The plenum method was discovered by Dr. Jean Jaubert and is often referred to as the Jaubert System. "Plenum" refers to an un-oxygenated layer of water trapped beneath a deep layer of gravel or sand at the bottom of an aquarium. This layer of water becomes anaerobic. Bacteria cultivate in this oxygen-free environment and remove nitrates from the aquarium. There are several variations of the plenum, depending on what literature you read.
The basic structure of the plenum system is essentially a deep (3" to 4") layer of gravel, suspended 1/2" to 1" above the bottom of an aquarium. It is usually recommended that very little or no water flow should be directed across the gravel surface. A basic plenum may be created by suspending egg crate material or under gravel filter plates above the aquarium bottom, using inert supports such as PVC pipe. If egg crate is used, it is covered with nylon screening over which the deep gravel bed is placed. The actual materials, including what grade of gravel or sand is used, vary depending on what literature you read, but usually coarse live sand, fine coral gravel, or a combination of both are used. One technique is to use 2" of live sand on the bottom, over which nylon screening is placed. The screen is then covered by 2" of fine coral gravel. This allows the aquarist to turn over the top inch of gravel occasionally to clean it, without disturbing the anaerobic layer below.
Anaerobic bacteria form in the bottom depths of the substrate and in the water below. As anaerobic bacteria cultivate, they remove nitrates. Anaerobic action produces a fair amount of heat. The heat warms the water layer below the gravel. The warmer water flows upwards, displacing cooler water above the gravel. This action moves water through the plenum at very slow rates. The slow movement of water through the gravel helps to prevent dangerous hydrogen-sulfide gases from forming in the plenum. The deep gravel bed also provides a home for burrowing motile invertebrates which feed on solid organic mulm and detritus. These burrowing animals, which are either purchased and/or cultivate on their own from live rock, serve to keep the plenum porous and aid in the slow movement of water through the system. "Burrowing" sea cucumbers that serve this function well may be purchased from a good aquarium store.
The aquarium is stocked with live rock, but not as much as is typically used. The live rock construct should be suspended above the gravel bed, allowing water to move freely beneath the reef. This may be accomplished in a number of ways. One way is to place a couple of "anchor" pieces on the gravel bed, and glue others to the back of the tank using aquarium epoxy putty (not silicone!). The rest of the live rock may then be bridged across these supports to build the reef, but not too high. The construct should be loose, not tightly packed together, to allow good flow through the rock. Care should be taken not to direct flow from pump returns across the gravel. The emphasis in aquariums using a plenum should be on the reef, with a minimal number of fish to balance the ecology.
The Jaubert Plenum System, if constructed properly, can work well, provided the aquarium is only lightly-stocked with fish. While we are sure some hobbyists would disagree with us here, we feel that more research is necessary on this fascinating subject. The original plenum method used aeration as the only means of water movement in the tank. We highly recommend that a plenum be used in conjunction with a Berlin system. The protein skimmer will remove other dissolved and solid organics, not removed by the plenum. The use of a protein skimmer combined with the plenum method may be the key to keeping more fish while using this type of biological filtration. If you're setting up a new aquarium, installing a plenum will be relatively easy. If you have an existing reef tank, installing a plenum will involve a fair to major amount of work. Definitely read up on the subject before you go to work.
Pumps
The rule of thumb is to pump the volume of the pond through the filter once an hour, with a higher turnover rate for small ponds (say, under 500 gallons) and a lower rate okay for larger ponds (say, over 2500 gallons). The pump must operate 24 hours a day in order to keep the bacteria alive. It is much better to have a smaller pump that is cheaper to operate running all the time than to have a larger pump that is shut off part of the day.
Sometimes a two-speed pump makes a lot of sense. It runs on low all the time to save energy costs and on high for back-washing or when a major water flow is desired. The new electromagnetic submersible pumps draw about one-seventh the energy of that of a similarly sized conventional pump, but they are limited in size.
What can go wrong?
If the bacteria colony is not thriving, ammonia will accumulate and algae will colonize the pond. The most common problems with bio filters (beyond poor design) are shutting off the pump for part of the day, improper cleaning, chlorine or chloramine in the water supply and copper leaching into the water from copper pipes. As previously noted, the pump must operate 24 hours a day. If the water source has chlorine or chloramine added, it can not be used to clean the filter as it will kill the bacteria. Furthermore, a chemical detoxifier must be added to the pond in an amount sufficient to treat new water added for topping up. If copper is present, it too must be detoxified with a proprietary water conditioner.
Both nitrifying and denitrifying bacteria should be added on a regular basis.
The sand in a pressurized filter should be checked after backwashing to ensure that it is clean. If not, a larger grain may be required.
This post first appeared on MAHSEER BREEDING And GOLD BULLION NEWS, please read the originial post: here
