Filter (aquarium)

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Air-driven corner filter Corner filter.jpg
Air-driven corner filter

Aquarium filters are critical components of both freshwater and marine aquaria. [1] [2] [3] Aquarium filters remove physical and soluble chemical waste products from aquaria, simplifying maintenance. Furthermore, aquarium filters are necessary to support life as aquaria are relatively small, closed volumes of water compared to the natural environment of most fish. [4]

Aquarium transparent tank of water for fish and water-dwelling species

An aquarium is a vivarium of any size having at least one transparent side in which aquatic plants or animals are kept and displayed. Fishkeepers use aquaria to keep fish, invertebrates, amphibians, aquatic reptiles such as turtles, and aquatic plants. The term "aquarium", coined by English naturalist Philip Henry Gosse, combines the Latin root aqua, meaning water, with the suffix -arium, meaning "a place for relating to". The aquarium principle was fully developed in 1850 by the chemist Robert Warington, who explained that plants added to water in a container would give off enough oxygen to support animals, so long as the numbers of animals did not grow too large. The aquarium craze was launched in early Victorian England by Gosse, who created and stocked the first public aquarium at the London Zoo in 1853, and published the first manual, The Aquarium: An Unveiling of the Wonders of the Deep Sea in 1854. An aquarium is a water-filled tank in which fish swim about. Small aquariums are kept in the home by hobbyists. There are larger public aquariums in many cities. This kind of aquarium is a building with fish and other aquatic animals in large tanks. A large aquarium may have otters, turtles, dolphins, and other sea animals. Most aquarium tanks also have plants.

Contents

Overview

Animals, typically fish, kept in fish tanks produce waste from excrement and respiration. Another source of waste is uneaten food or plants and fish which have died. These waste products collect in the tanks and contaminate the water. As the degree of contamination rises, the risk to the health of the aquaria increases and removal of the contamination becomes critical. Filtration is a common method used for maintenance of healthy aquaria.

Biological filtration and the nitrogen cycle

A large shower biological filter designed to maximize the beneficial effects of the nitrogen cycle, in a koi pond KoiPondTrickleFilter.jpg
A large shower biological filter designed to maximize the beneficial effects of the nitrogen cycle, in a koi pond

Proper management of the nitrogen cycle is a vital element of a successful aquarium. Excretia and other decomposing organic matter produce ammonia which is highly toxic to fish. Bacterial processes oxidize this ammonia into the slightly less toxic nitrites, and these are in turn oxidized to form the much less toxic nitrates. In the natural environment these nitrates are subsequently taken up by plants as fertilizer and this does indeed happen to some extent in an aquarium planted with real plants.

Nitrogen cycle biogeochemical cycle by which nitrogen is converted into various chemical forms

The nitrogen cycle is the biogeochemical cycle by which nitrogen is converted into multiple chemical forms as it circulates among atmosphere, terrestrial, and marine ecosystems. The conversion of nitrogen can be carried out through both biological and physical processes. Important processes in the nitrogen cycle include fixation, ammonification, nitrification, and denitrification. The majority of Earth's atmosphere (78%) is atmosphere nitrogen, making it the largest source of nitrogen. However, atmospheric nitrogen has limited availability for biological use, leading to a scarcity of usable nitrogen in many types of ecosystems.

Ammonia Chemical compound of nitrogen and hydrogen

Ammonia is a compound of nitrogen and hydrogen with the formula NH3. The simplest pnictogen hydride, ammonia is a colourless gas with a characteristic pungent smell. It is a common nitrogenous waste, particularly among aquatic organisms, and it contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or indirectly, is also a building block for the synthesis of many pharmaceutical products and is used in many commercial cleaning products. It is mainly collected by downward displacement of both air and water. Ammonia is named for the Ammonians, worshipers of the Egyptian god Amun, who used ammonium chloride in their rituals.

An aquarium is, however, an imperfect microcosm of the natural world. Aquariums are usually much more densely stocked with fish than the natural environment. This increases the amount of ammonia produced in the relatively small volume of the aquarium. The bacteria responsible for breaking down the ammonia colonize the surface of any objects inside the aquarium. In most cases, a biological filter is nothing more than a chemically inert porous sponge, which provides a greatly enlarged surface area on which these bacteria can develop. These bacterial colonies take several weeks to form, during which time the aquarium is vulnerable to a condition commonly known as "new tank syndrome" if stocked with fish too quickly. Some systems incorporate bacteria capable of converting nitrates into nitrogen gas. [5]

Accumulation of toxic ammonia from decomposing wastes is the largest cause of fish mortality in new, poorly maintained, or overloaded aquariums. [6] In the artificial environment of the aquarium, the nitrogen cycle effectively ends with the production of nitrates. In order that the nitrate level does not build up to a harmful level regular partial water changes are required to remove the nitrates and introduce new, uncontaminated water. [7]

Mechanical and chemical filtration

The process of mechanical filtration removes particulate material from the water column. This particulate matter may include uneaten food, feces or plant or algal debris. Mechanical filtration is typically achieved by passing water through materials which act as a sieve, physically trapping the particulate matter. [1] Removal of solid waste can be as simple as physical hand netting of debris, and/or involve highly complex equipment. All removal of solid wastes involve filtering water through some form of mesh in a process known as mechanical filtration. The solid wastes are first collected, and then must be physically removed from the aquarium system. Mechanical filtration is ultimately ineffective if the solid wastes are not removed from the filter, and are allowed to decay and dissolve in the water.

Dissolved wastes are more difficult to remove from the water. Several techniques, collectively known as chemical filtration, are used for the removal of dissolved wastes, the most popular being the use of activated carbon and foam fractionation. To a certain extent, healthy plants extract dissolved chemical wastes from water when they grow, so plants can serve a role in the containment of dissolved wastes.

A final and less common situation requiring filtration involves the desire to sterilize water-borne pathogens. This sterilization is accomplished by passing aquarium water through filtration devices which expose the water to high intensity ultraviolet light and/or exposing the water to dissolved ozone gas.

Materials suitable for aquarium filtration

Sponges, plastic balls, ceramic tubes and gravel are all suitable for aquarium filtration Filtermaterial 060227.jpg
Sponges, plastic balls, ceramic tubes and gravel are all suitable for aquarium filtration

Numerous materials are suitable as aquarium filtration media. These include synthetic wools, known in the aquarium hobby as filter wool, made of polyethylene terephthalate or nylon. Synthetic sponges or foams, various ceramic and sintered glass and silicon products along with igneous gravels are also used as mechanical filter materials. Materials with a greater surface area provide both mechanical and biological filtration. Some filter materials, such as plastic "bioballs", are best used for biological filtration.

With the notable exception of diatom filters, aquarium filters are rarely purely mechanical in action, as bacteria will colonise most filter materials effecting some degree of biological filtration. [1] Activated carbon and zeolites are also frequently added to aquarium filters. These highly porous materials act as adsorbates binding various chemicals to their large external surfaces [2] and also as sites of bacterial colonisation.

The simplest type of aquarium filter consists only of filter wool and activated carbon. The filter wool traps large debris and particles, and the activated carbon adsorbs smaller impurities. These should be changed regularly at suitable intervals. [8] This is particularly important in the case of activated carbon filters, which may re-release their adsorbed contents in large (and therefore harmful) doses if they are allowed to saturate. [9] Activated carbon adsorbs toxins on the extended porous surface of the carbon. It cannot be reactivated by boiling in water. The adsorption of activated carbon can be restored by thermal regeneration at temperatures of 500–900 °C (932–1,652 °F), [10] electrochemical regeneration, ultrasound, or other industrial processes. For the aquarist, replacing the activated carbon with fresh material is simple and inexpensive.

Types of aquarium filters

A commercially available canister filter Aquarium - external filter.jpg
A commercially available canister filter

Numerous types of aquarium filters are commercially available, [11] including:

Power filters

Power or HOB (hang on back) filters, which are impeller powered, remove water from the aquarium, usually with a long siphoning tube, which is then pushed (or pulled) through a series of different filter media and returned to the aquarium. These are the most common type of aquarium filter. [1] They are usually more effective and easier to maintain than internal filters. [12]

Advantages of this type of filter are that they allow for a selection of different types of filter media depending on the tank needs, and that they are easy to clean without disturbing the inhabitants of the tank because they sit on the outside of the fish tank. Disadvantages of power filters include their smaller capacity for filter media compared to canister filters, and that they tend to be very noisy, usually resulting from vibrations. [13]

Canister filters

Compared to filters that hang on the back of the aquarium, canister-style external filters offer a greater quantity of filter materials to be used along with a greater degree of flexibility with respect to filter material choice. [2] Water enters the canister filled with the chosen filter material through an intake pipe at the bottom of the canister, passes through the material, and is fed back to the aquarium through the return pipe. Water is forced to circulate through the filter by a pump typically installed at the top of the canister. It is important to note that canister filters are sealed, fully flooded systems, meaning that the aquarium, intake pipe, filter interior and the return pipe form a continuous body of water. In this configuration both the intake and return path form two siphons, which precisely counterbalance each other. Under these circumstances, the filter pump does not have to spend any effort to lift the water back to the aquarium, regardless of how high the latter is installed above the canister. The pump should only be powerful enough to push the water through the filtering material as well as overcome the drag in the intake and return pipes. This makes canister filter pumps virtually insensitive to the height difference between the aquarium and the filter (although exceeding the manufacturer-specified height limit can lead to leaks).

Benefits of this type of filter are that they can provide a high volume of filter material without reducing the internal space in the aquarium, and that they can be disconnected from the tank for cleaning/maintenance and replaced without disturbing the aquarium interior or occupants. Also, as a filter with external plumbing, it supports in-line installation of other aquarium equipment, such as water heaters and carbon dioxide diffusers. Such equipment can be removed from the tank and installed in-line into the return pipe of the filter. Disadvantages of canister filters include the increased cost and complexity relative to internal filters and difficulties in cleaning the tubes which transfer water to and from the aquarium. [3] There is also the risk of a leak, which naturally is an issue for any filter placed outside of the aquarium.

Canister filters were initially designed to filter drinking water, under low pressure. Canister filters for aquariums use high water pressure, from a properly powered pump, to force water through the dense filter media. A pump can draw water from an under-gravel filter, and run it into a canister for double filtration.

Diatom filters

Diatom filters are used only for sporadic cleaning of tanks, they are not continuously operated on aquariums. These filters utilise diatomaceous earth to create an extremely fine filter down to 1 µm which removes particulate matter from the water column. [1]

Trickle filters

Trickle filters, also known as wet/dry filters are another water filtration systems for marine and freshwater aquariums. [12] This filter comes in two configurations, one which is placed on top of the aquarium (more rarely seen) and one which is placed below the aquarium (more common).

If the wet/dry filter is placed on top of the aquarium, water is pumped over a number of perforated trays containing filter wool or some other filter material. The water trickles through the trays, keeping the filter wool wet but not completely submerged, allowing aerobic bacteria to grow and aiding biological filtration. The water returns to the aquarium like rain. [12]

Alternatively, the wet/dry filter may be placed below the tank. In this design, water is fed by gravity to the filter below the aquarium. Prefiltered water is delivered to a perforated plate (drip plate). Prefiltering may take place in the aquarium via a foam block or sleeve in the overflow, or weir siphon, or it may be prefiltered by filter wool resting on the perforated plate. The waste laden water from the aquarium spreads over the drip plate, and rains down through a medium. This may be a filter wool/plastic grid rolled into a circular shape (DLS or "Double Layer Spiral") or any number of plastic media commonly known as Bio Balls. As the water cascades over the media, CO2 is given off, oxygen is picked up, and bacteria convert the waste from the tank into less harmful materials. From here the water enters the sump. The sump may contain a number of compartments, each with its own filtration material. Often, heaters and thermostats are placed in the sump. [12]

Algae filters

Algae scrubber (upflow version) floating on a reef pond Modern floating surface algae scrubber filter, floating on top of aquarium.jpg
Algae scrubber (upflow version) floating on a reef pond

Algae may be grown purposely, which removes chemicals from the water which need to be removed in order to have healthy fish, invertebrates and corals. This is a natural ("green") filtering method, which lets an aquarium operate the way oceans and lakes operate. [14]

Algae and disease-causing organisms can also be removed by treating the water with ultraviolet irradiation, but the drawback of UV is that it will kill beneficial bacteria as well. Therefore, UV treatment is typically used only when needed, and not all the time.

Baffle filters

A newly set up baffle filter, under a large volume cichlid aquarium Baffle filter.JPG
A newly set up baffle filter, under a large volume cichlid aquarium

Baffle filters are similar to wet and dry, trickle filters in that they are generally situated below the aquarium. This type of filter consists of a series of baffles that the water must pass through in order to reach the pump which is returning water to the aquarium. These baffles then act much like a series of canister filters and can be filled with different filter media for different purposes. [15]

Fluidized bed filter

Simple DIY fluidized sand bed filter Fluidized.jpg
Simple DIY fluidized sand bed filter

The fluidized bed filter (FBF) is a biological reactor only. The principle is to direct water through a sand (or similar media) bed from below so that the sand becomes fluidized – behaves like a fluid. This mechanism is seen in liquefaction, quick sand, and industrial processes including municipal sewage treatment. The combined surface of all sand particles in the filter is very large, and so there is a large surface for aerobic denitrification bacteria. Therefore, the size of the filter can be modest.

The filter itself can be internal or external. In its simplest DIY internal version an FBF is very easy to build, with a container, sand, pump, and some plumbing. There are many variables: shape and size of the container, quantity of sand or equivalent, particle sizes, the pump's power, and plumbing.

Internal filters

An internal aquarium filter driven by air displacement Internal filter2.jpg
An internal aquarium filter driven by air displacement

Internal filters are, by definition, filters within the confines of the aquarium. These include the sponge filter, variations on the corner filter (pictured top right and left), foam cartridge filter and the undergravel filter. [1] An internal filter may have an electric pump and thus be an internal power filter, often attached to the inside of aquaria via suction cups.

Airlift filters

Sponge filters and corner filters (sometimes called box filters) work by essentially the same mechanism as an internal filter. Both generally work by airlift, using bubbles from an air pump rising in a tube to create flow. In a sponge filter, the inlet may only be covered by a simple open-cell block of foam. A corner filter is slightly more complex. These filters are often placed in the corner on the bottom of the aquarium. Water enters slits in the box, passes through a layer of medium, then exits through the airlift tube to return to the aquarium. These filters tend to only be suitable for small and lightly stocked aquaria. The sponge filter is especially useful for rearing fry where the sponge prevents the small fish from entering the filter. [12]

Undergravel filters

A schematic diagram of an undergravel filter run by both an air displacement and water pump (powerhead) Undergravel filter.svg
A schematic diagram of an undergravel filter run by both an air displacement and water pump (powerhead)

One of the oldest types of filters, the undergravel filters consist of a porous plate which is placed beneath the gravel on the base of the aquarium and one, or more, uplift tubes. Historically, undergravel filters have been driven via air displacement. Air stones are placed at the base of uplift tubes which force water out of the uplift tube creating negative pressure beneath the undergravel filter plate (also called the plenum). [16] Water then percolates down through the gravel which itself is the filtration material. [1] Greater flow rate of water through the gravel can be achieved via the use of water pump rather than air displacement. [1]

Beneficial bacteria colonize the gravel bed and provide biological filtration, using the substrate of the aquarium itself as a biological filter. [8] [12]

Undergravel filters can be detrimental to the health of aquatic plants. [8] Fine substrates such as sand or peat may clog an undergravel filter. [12] Undergravel filters are not effective if the substrate bed is uneven. In an uneven gravel bed, water will flow only through the thin portions of the bed, leaving the more heavily covered areas to become anoxic.

Marine-specific systems

Protein skimmers

Deep sand beds

Berlin method

Related Research Articles

Filtration process that separates solids from fluids

Filtration is any of various mechanical, physical or biological operations that separate solids from fluids by adding a medium through which only the fluid can pass. The fluid that passes through is called the filtrate. In physical filters oversize solids in the fluid are retained and in biological filters particulates are trapped and ingested and metabolites are retained and removed. However, the separation is not complete; solids will be contaminated with some fluid and filtrate will contain fine particles. Filtration occurs both in nature and in engineered systems; there are biological, geological, and industrial forms. For example, in animals, renal filtration removes waste from the blood, and in water treatment and sewage treatment, undesirable constituents are removed by absorption into a biological film grown on or in the filter medium, as in slow sand filtration.

Water filter water filter

A water filter removes impurities by lowering contamination of water using a fine physical barrier, a chemical process, or a biological process. Filters cleanse water to different extents for purposes such as providing agricultural irrigation, accessible drinking water, public and private aquariums, and the safe use of ponds and swimming pools.

Reef aquarium

A reef aquarium or reef tank is a marine aquarium that prominently displays live corals and other marine invertebrates as well as fish that play a role in maintaining the tropical coral reef environment. A reef aquarium requires appropriately intense lighting, turbulent water movement, and more stable water chemistry than fish-only marine aquaria, and careful consideration is given to which reef animals are appropriate and compatible with each other.

Protein skimmer

A protein skimmer or foam fractionator is a device used to remove organic compounds such as food and waste particles from water. It is most commonly used in commercial applications like municipal water treatment facilities and public aquariums. Smaller protein skimmers are also used for filtration of home saltwater aquariums.

Marine aquarium

A marine aquarium is an aquarium that keeps marine plants and animals in a contained environment. Marine aquaria are further subdivided by hobbyists into fish only (FO), fish only with live rock (FOWLR), and reef aquaria. Fish only tanks often showcase large or aggressive marine fish species and generally rely on mechanical and chemical filtration. FOWLR and reef tanks use live rock, a material composed of coral skeletons harboring beneficial nitrogen waste metabolizing bacteria, as a means of more natural biological filtration.

Constructed wetland An artificial wetland to treat municipal or industrial wastewater, greywater or stormwater runoff

A constructed wetland (CW) is an artificial wetland to treat municipal or industrial wastewater, greywater or stormwater runoff. It may also be designed for land reclamation after mining, or as a mitigation step for natural areas lost to land development.

Sand filter sand

Sand filters are used as a step in the water treatment process of water purification.

The Berlin Method of biological filtration is a method for maintaining a clean and stable environment within a saltwater aquarium, typically a coral reef system. This method relies on the use of ample live rock. The theory is that aerobic bacteria covering the surface of the porous live rock and sand convert harmful ammonia into nitrites, then nitrates, which are much less harmful to the tank's inhabitants. Through the process of diffusion, the nitrates move deep within the rock where they are converted by anaerobic bacteria to free nitrogen gas. Left over nitrates are removed through regular partial water changes. As an added measure, a protein skimmer is used to remove some of the dissolved organic compounds before they break down into ammonia.

Community aquaria are tanks that are designed to contain more than one species of fish. Most commonly they include a variety of species that do not normally occur together in nature, for example angelfish from Brazil, swordtails from Mexico, and gouramis from South East Asia. The aim of such communities is to bring together fish that are compatible in temperament and water requirements, while using their different colours and behaviours to add interest and entertainment value.

Fishkeeping hobby practiced by aquarists

Fishkeeping is a popular hobby, practiced by aquarists, concerned with keeping fish in a home aquarium or garden pond. There is also a piscicultural fishkeeping industry, as a branch of agriculture.

Detritus Dead particulate organic material

In biology, detritus is dead particulate organic material. It typically includes the bodies or fragments of dead organisms as well as fecal material. Detritus is typically colonized by communities of microorganisms which act to decompose the material. In terrestrial ecosystems, it is encountered as leaf litter and other organic matter intermixed with soil, which is denominated "soil organic matter". Detritus of aquatic ecosystems is organic material suspended in water and piling up on seabed floors, which is referred to as marine snow.

Common goldfish

The common goldfish is a breed of goldfish with no other differences from its living ancestor, the Prussian carp, other than its color and shape. Goldfish are a form of domesticated wild carp and are a close relative of koi. Most varieties of fancy goldfish were derived from this simple breed. Common goldfish come in a variety of colors including red, orange, red/white, white/black, grey/brown/, olive green, yellow, white, black, and calico kind, with the most common variation being orange ,(combined with its simplicity, hence the name). Sometimes, the brightness, duration, and the vividness of the color may be an indication of the fish’s health status.

Koi pond

Koi ponds are ponds used for holding koi, usually as part of a landscape. Koi ponds can be designed specifically to promote health and growth of the Nishikigoi or Japanese Ornamental Carp. The architecture of the koi pond can have a great effect on the health and well being of the koi. The practice of keeping koi often revolves around "finishing" a koi at the right time. The concept of finishing means that the fish has reached its highest potential. Koi clubs hold shows where koi keepers bring their fish for judging.

Substrate (aquarium) material used on the tank bottom of an aquarium

The substrate of an aquarium refers to the material used on the tank bottom. It can affect water chemistry, filtration, and the well-being of the aquarium's inhabitants, and is also an important part of the aquarium's aesthetic appeal. The appropriate substrate depends on the type of aquarium; the most important parameter is whether the aquarium contains fresh water or saltwater.

Freshwater aquarium

A freshwater aquarium is a receptacle that holds one or more freshwater aquatic organisms for decorative, pet-keeping, or research purposes. Modern aquariums are most often made from transparent glass or acrylic glass. Typical inhabitants include fish, plants, amphibians, and invertebrates, such as snails and crustaceans.

Trickling filter Type of wastewater treatment system with a fixed bed of rocks or similar

A trickling filter is a type of wastewater treatment system. It consists of a fixed bed of rocks, coke, gravel, slag, polyurethane foam, sphagnum peat moss, ceramic, or plastic media over which sewage or other wastewater flows downward and causes a layer of microbial slime (biofilm) to grow, covering the bed of media. Aerobic conditions are maintained by splashing, diffusion, and either by forced-air flowing through the bed or natural convection of air if the filter medium is porous.

Sewage treatment Process of removing contaminants from municipal wastewater

Sewage treatment is the process of removing contaminants from municipal wastewater, containing mainly household sewage plus some industrial wastewater. Physical, chemical, and biological processes are used to remove contaminants and produce treated wastewater that is safe enough for release into the environment. A by-product of sewage treatment is a semi-solid waste or slurry, called sewage sludge. The sludge has to undergo further treatment before being suitable for disposal or application to land.

An aquarium powerhead is a water pump completely submerged into an aquarium to circulate water.

Recirculating aquaculture system

Recirculating aquaculture systems (RAS) are used in home aquaria and for fish production where water exchange is limited and the use of biofiltration is required to reduce ammonia toxicity. Other types of filtration and environmental control are often also necessary to maintain clean water and provide a suitable habitat for fish. The main benefit of RAS is the ability to reduce the need for fresh, clean water while still maintaining a healthy environment for fish. To be operated economically commercial RAS must have high fish stocking densities, and many researchers are currently conducting studies to determine if RAS is a viable form of intensive aquaculture.

References

  1. 1 2 3 4 5 6 7 8 Riehl, Rüdiger. Editor.; Baensch, HA (1996). Aquarium Atlas (5th ed.). Germany: Tetra Press. ISBN   3-88244-050-3.CS1 maint: Extra text: authors list (link)
  2. 1 2 3 Leibel WS (1993) A fishkeepers guide to South American cichlids. Tetra Press. Belgium pg 12-14.
  3. 1 2 Loiselle, Paul V. (1995). The Cichlid Aquarium. Germany: Tetra Press. ISBN   1-56465-146-0.
  4. ↑ Sands D (1994) A fishkeepers guide to Central American cichlids. Tetra Press. Belgium pg 17-19.
  5. ↑ http://www.aquariumslife.com/diy-projects/diy-aquariumdenitrator
  6. ↑ Patrick T. K. Woo; David W. Bruno (2002). Diseases and disorders of finfish in cage culture. Wallingford, Oxon, UK: CABI Pub. p. 284. ISBN   0-85199-443-1.
  7. ↑ http://www.aquacadabra.com/blog/the-basics-of-filtration
  8. 1 2 3 Axelrod, Herbert, R. (1996). Exotic Tropical Fishes. T.F.H. Publications. ISBN   0-87666-543-1.
  9. ↑ Eade, Andrew (1999). Coldwater Fishkeeping. Ringpress Books. p. 33. ISBN   1-86054-072-4.
  10. ↑ Sabio, E.; Gonzalez, E.; Gonzalez, J. F.; Gonzalez-Garcia, C. M.; Ramiro, A.; Ganan, J (2004). "Thermal regeneration of activated carbon saturated with p-nitrophenol". Carbon. 42 (11): 2285–2293. doi:10.1016/j.carbon.2004.05.007.
  11. ↑ Mary Bailey; Nick Dakin (2001). The Aquarium Fish Handbook. New Holland Publishers. p. 26. ISBN   978-1-85974-190-0.
  12. 1 2 3 4 5 6 7 Sanford, Gina (1999). Aquarium Owner's Guide. New York: DK Publishing. pp. 164–167. ISBN   0-7894-4614-6.
  13. ↑ "Freshwater Aquarium Filters – Aquarium Fish Hub". aquariumfishhub.com. Retrieved 2017-06-14.
  14. ↑ Nutrient Cycling In The Great Barrier Reef Aquarium. Proceedings of the 6th International Coral Reef Symposium, Australia, 1988, Vol. 2
  15. ↑ Sandford G, Crow R (1991) The Manual of Tank Busters. Tetra Press, USA
  16. ↑ Spotte, Stephen (1993-07-30). Marine Aquarium Keeping. John Wiley & Sons. pp. 25–. ISBN   9780471594895 . Retrieved 14 October 2014.
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