Aquarium filters are critical components of both freshwater and marine aquaria. 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.
Overview edit
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 edit
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.
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.
Accumulation of toxic ammonia from decomposing wastes is the largest cause of fish mortality in new, poorly maintained, or overloaded aquariums. 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.
Mechanical and chemical filtration edit
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. 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 involves filtering water through some form of a 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 edit
Numerous materials are suitable for 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 "bio-balls", are best used for biological filtration.
With the notable exception of diatom filters, aquarium filters are rarely purely mechanical in action, as bacteria will colonize most filter materials, effecting some degree of biological filtration. 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 and also as sites of bacterial colonization.
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. 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. 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), 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 edit
Numerous types of aquarium filters are commercially available, including:
Power filters edit
Power or HOB (hang on back) filters, typically powered by an impeller, remove water from the aquarium, which is then pushed (or pulled) through a series of different filter media and returned to the aquarium. These are the most common filter. They are usually more effective and easier to maintain than internal filters.
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 noise resulting from vibrations.
Canister filters edit
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. 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 the 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. 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 edit
Diatom filters are used only for sporadic cleaning of tanks, they are not continuously operated on aquariums. These filters utilize diatomaceous earth to create an extremely fine filter down to 1 µm which removes particulate matter from the water column.
Trickle filters edit
Trickle filters, also known as wet/dry filters are another water filtration systems for marine and freshwater aquariums. 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.
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.
Algae filters edit
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.
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 edit
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.
Fluidized bed filter edit
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 edit
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 under gravel filter. 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 edit
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.
Under gravel filters edit
One of the oldest types of filters, the under gravel 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, under gravel 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 under gravel filter plate (also called the plenum). Water then percolates down through the gravel which itself is the filtration material. A greater flow rate of water through the gravel can be achieved via the use of water pump rather than air displacement.
Beneficial bacteria colonize the gravel bed and provide biological filtration, using the substrate of the aquarium itself as a biological filter.
Undergravel filters can be detrimental to the health of aquatic plants. Fine substrates such as sand or peat may clog an under gravel filter. 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 edit
Protein skimmers edit
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.
Function edit
Protein skimming removes certain organic compounds, including proteins and amino acids found in food particles, by using the polarity of the protein itself. Due to their intrinsic charge, water-borne proteins are either repelled or attracted by the air/water interface and these molecules can be described as hydrophobic (such as fats or oils) or hydrophilic (such as salt, sugar, ammonia, most amino acids, and most inorganic compounds). However, some larger organic molecules can have both hydrophobic and hydrophilic portions. These molecules are called amphipathic or amphiphilic. Commercial protein skimmers work by generating a large air/water interface, specifically by injecting large numbers of bubbles into the water column. In general, the smaller the bubbles the more effective the protein skimming is because the surface area of small bubbles occupying the same volume is much greater than the same volume of larger bubbles. Large numbers of small bubbles present an enormous air/water interface for hydrophobic organic molecules and amphipathic organic molecules to collect on the bubble surface (the air/water interface). Water movement hastens diffusion of organic molecules, which effectively brings more organic molecules to the air/water interface and lets the organic molecules accumulate on the surface of the air bubbles. This process continues until the interface is saturated unless the bubble is removed from the water or it bursts, in which case the accumulated molecules release back into the water column. However, it is important to note that further exposure of a saturated air bubble to organic molecules may continue to result in changes as compounds that bind more strongly may replace those molecules with a weaker binding that have already accumulated on the interface. Although some aquarists believe that increasing the contact time (or dwell time as it is sometimes called) is always good, it is incorrect to claim that it is always better to increase the contact time between bubbles and the aquarium water. As the bubbles increase near the top of the protein skimmer water column, they become denser and the water begins to drain and create the foam that will carry the organic molecules to the skimmate collection cup or to a separate skimmate waste collector and the organic molecules, and any inorganic molecules that may have become bound to the organic molecules, will be exported from the water system.
In addition to the proteins removed by skimming, there are a number of other organic and inorganic molecules that are typically removed. These include a variety of fats, fatty acids, carbohydrates, metals such as copper, and trace elements such as iodine. Particulates, phytoplankton, bacteria, and detritus are also removed; this is desired by some aquarists and is often enhanced by placement of the skimmer before other forms of filtration, lessening the burden on the filtration system as a whole. There is at least one published study that provides a detailed list of the export products removed by the skimmer. Aquarists who keep filter-feeding invertebrates, however, sometimes prefer to keep these particulates in the water to serve as natural food.
Protein skimmers are used to harvest algae and phytoplankton gently enough to maintain viability for culturing or commercial sale as live cultures.
Alternative forms of water filtration have recently come into use, including the algae scrubber, which leaves food particles in the water for corals and small fish to consume, but removes the noxious compounds including ammonia, nitrite, nitrate, and phosphate that protein skimmers do not remove.
Design edit
All skimmers have key features in common: water flows through a chamber and is brought into contact with a column of fine bubbles. The bubbles collect proteins and other substances and carry them to the top of the device where the foam, but not the water, collects in a cup. Here the foam condenses to a liquid, which can be easily removed from the system. The material that collects in the cup can range from pale greenish-yellow, watery liquid to a thick black tar.
Consider this summary of optimal protein skimmer design by Randy Holmes-Farley:
For a skimmer to function maximally, the following things must take place:
1. A large amount of air/water interface must be generated.
2. Organic molecules must be allowed to collect at the air/water interface.
3. The bubbles forming this air/water interface must come together to form a foam.
4. The water in the foam must partially drain without the bubbles popping prematurely.
5. The drained foam must be separated from the bulk water and discarded.
Also under considerable recent attention has been the general shape of a skimmer as well. In particular, much attention has been given to the introduction of cone-shaped skimmer units. Originally designed by Klaus Jensen in 2004, the concept was founded on the principle that a conical body allows the foam to accumulate more steadily through a gently sloping transition. This reduces the overall turbulence, resulting in more efficient skimming. While research into the specific benefits of the design is still being measured, early reviews of many conical skimmers have been positive overall.
Overall, protein skimmers can be classed in two ways depending on whether they operate by co-current flow or counter-current flow. In a co-current flow system, air is introduced at the bottom of the chamber and is in contact with the water as it rises upwards towards the collection chamber. In a counter-current system, air is forced into the system under pressure and moves against the flow of the water for a while before it rises up towards the collection cup. Because the air bubbles may be in contact with the water for a longer period in a counter-current flow system, protein skimmers of this type are considered by some to be more effective at removing organic wastes.
Co-current flow systems edit
- Air stone
The original method of protein skimming, running pressurized air through a diffuser to produce large quantities of microbubbles, remains a viable, effective, and economic choice, although newer technologies may require lower maintenance. The air stone is most often an oblong, partially hollowed block of wood, most often of the genus Tilia. The most popular wooden air-stones for skimmers are made from limewood (Tilia europaea or European limewood) although basswood (Tilia americana or American Linden), works as well, may be cheaper and is often more readily available. The wooden blocks are drilled, tapped, fitted with an air fitting, and connected by air tubing to one or more air pumps delivering at least 1 CFM. The wooden air stone is placed at the bottom of a tall column of water. The tank water is pumped into the column, allowed to pass by the rising bubbles, and back into the tank. To get enough contact time with the bubble, these units can be many feet in height.
Air stone protein skimmers may be constructed as a DIY project from PVC pipes and fittings at low cost [1] [2] and with varying degrees of complexity [3].
While this method has been around for many years, many regard it as inefficient for larger systems or systems with large bio-loads.
- Venturi
The premise behind these skimmers is that a venturi pump, or aspirator, can be used to introduce the bubbles into the water stream. The tank water is pumped through the venturi, in which fine bubbles are introduced, then enters the skimmer body. This method was popular due to its compact size and high efficiency but venturi designs are now more likely to be included in other skimmer designs rather than as a simple venturi design.
Counter-current flow systems edit
- Aspirating: pin-wheel/Adrian-wheel, needle-wheel, mesh-wheel
This basic concept is more correctly known as an aspirating skimmer since some skimmer designs using an aspirator do not use a "Pin-Wheel"/"Adrian-Wheel" or "Needle-Wheel". "Pin-Wheel"/"Adrian-Wheel" describes the look of an impeller that consists of a disk with pins mounted perpendicular (90°) to the disc and parallel to the rotor. "Needle-Wheel" describes the look of an impeller that consists of a series of pins projecting out perpendicular to the rotor from a central axis. "Mesh-Wheel" describes the look of an impeller that consists of a mesh material attached to a plate or central axis on the rotor. The purpose of these modified impellers is to chop or shred the air that is introduced via a venturi apparatus or external air pump into very fine bubbles. The Mesh-Wheel design is fairly new and, while providing excellent results in the short term because of its ability to draw in more air and create finer bubbles with its thin cutting surfaces, it is still being developed and will likely continue to evolve over a few more years.
This style of protein skimmer has become very popular and is believed to be the most popular type of skimmer used with residential reef aquariums today. It has been particularly successful in smaller aquariums due to its usually compact size, ease of setting up and use, and quiet operation. Since the pump is pushing a mixture of air and water, the power required to turn the rotor can be decreased and may result in a lower power requirement for that pump vs. the same pump with a different impeller when it is only pumping water.
- Downdraft
The Downdraft skimmer is both a proprietary skimmer design and a style of protein skimmer that injects water under high pressure into tubes that have a foam or bubble generating mechanism and carry the air/water mixture down into the skimmer and into a separate chamber. The proprietary design is protected in the United States with patents and commercial skimmer products in the US are limited to that single company. Their design uses one or more tubes with plastic media such as bio balls inside to mix water under high pressure and air in the body of the skimmer resulting in foam that collects protein waste in a collection cup. This was one of the earlier high-performance protein skimmer designs and large models were produced that saw success in large and public aquariums.
- Beckett skimmer
The Beckett skimmer has some similarities to the downdraft skimmer but introduced a foam nozzle to produce the flow of air bubbles. The name Beckett comes from the patented foam nozzle developed and sold by the Beckett Corporation (United States), although similar foam nozzle designs are sold by other companies outside the United States (e.g. Sicce (Italy)). Instead of using the plastic media that is found in downdraft skimmer designs, the Beckett skimmer uses design concepts from previous generations of skimmers, specifically the downdraft skimmer and the venturi skimmer (the Beckett 1408 Foam Nozzle is a modified 4 port venturi) to produce a hybrid that is capable of using powerful pressure rated water pumps and quickly processing large amounts of aquarium water in a short period of time. Commercial Beckett skimmers come in single Beckett, dual Beckett, and quad Beckett designs. Well engineered Beckett skimmers are quiet and reliable but the powerful pumps used in larger Beckett skimmer designs can take up additional space, introduce additional noise, and use more electricity than less powerful pumps. Unlike the Downdraft and Spray Induction skimmers, Beckett skimmer designs are produced by a number of companies in the United States and elsewhere and are not known to be restricted by patents.
- Spray induction
This method is related to the downdraft, but uses a pump to power a spray nozzle, fixed a few inches above the water level. The spray action entraps and shreds the air in the base of the unit, which then rises to the collection chamber. In the United States, one company has patented the spray induction technology and the commercial product offerings are limited to that single company.
Recirculating skimmer designs edit
A recent trend is to change the method by which the skimmer is fed 'dirty' water from the aquarium as a means to recirculate water within the skimmer multiple times before it is returned to the sump or the aquarium. Aspirating pump skimmers are the most popular type of skimmer to use recirculating designs although other types of skimmers, such as Beckett skimmers, are also available in recirculating versions. While there is a popular belief among some aquarist that this recirculation increases the dwell or contact time of the generated air bubbles within the skimmer there is no authoritative evidence that this is true. Each time water is recirculated within the skimmer any air bubbles in that water sample are destroyed and new bubbles are generated by the recirculating pump venturi apparatus so the air-water contact time begins again for these newly created bubbles. In non-recirculating skimmer designs, a skimmer has one inlet supplied by a pump that pulls water in from the aquarium and injects it with air into the skimmer and releasing the foam or air/water mix into the reaction chamber. With a recirculating design, the one inlet is usually driven by a separate feed pump, or in some cases may be gravity fed, to receive the dirty water to process, while the pump providing the foam or air/water mix into the reaction chamber is set up separately in a closed loop on the side of the skimmer. The recirculating pump pulls water out of the skimmer and injects air to generate the foam or air/water mix before returning it to the skimmer reaction chamber—thus 'recirculating' it. The feed pump in a recirculating design typically injects a smaller amount of dirty water than co/counter-current designs. The separate feed pump allows easy control of the rate of water exchange through the skimmer and for many aquarists, this is one of the important attractions of recirculating skimmer designs. Because the pump configuration of these skimmers is similar to that of aspirating pump skimmers, the power consumption advantages are also similar.
Deep sand beds edit
A deep sand bed is a filtration method used in some saltwater aquariums. A deep sand bed, similar to the Berlin Method, is designed to cultivate anaerobic bacteria in the bottom layers of sand, converting nitrate to nitrogen gas to remove toxic nitrates.
Operation edit
A deep sand bed is commonly defined as a bed of fine sand with a minimum depth of four to six inches which ensures that a portion of the sand at the bottom will not be exposed to the significant circulation of water. An established deep sand bed consists of sand populated with bacteria, algae and other marine organisms such as worms, crabs, snails, and stars. The creatures burrow and overturn the top two to three inches of sand in search of food, which causes water to circulate deeper in the sand than it would if the creatures were not present.
Deep sand beds may be made of a variety of materials, but typically fine or superfine sand is used, with a grain size between 1 mm and 0.05 mm. A larger particle size increases circulation, which in turn requires greater depth to establish anaerobic areas. Larger particles can also inhibit the burrowing of small animals, which would limit circulation into the bed. Additionally, larger particles (2 mm or larger) are prone to detritus accumulation, which necessitates periodic siphon cleaning.
Berlin method edit
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 (rock with live marine organisms and bacteria on or in it). The theory is that aerobic bacteria covering the surface of the porous live rock and sand convert harmful ammonia (from fish and invertebrate waste) 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. Leftover 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.
The typical rule of thumb is to use from 1-2 lb (.45 to .9 kg) of live rock per gallon (US) (~ 5 liters) of aquarium water depending on the density of the rock – or filling the tank up 2/3 of the way to the top. The benefit of using live rock is fourfold: First, live rock acts as a biological filter, adding beneficial bacteria. Secondly, it introduces an abundance of marine life into the aquarium that many fish, invertebrates and corals use as food. Thirdly, it provides a natural reef appearance with ample places to locate corals. Lastly, live rock will also help balance and stabilize pH in the aquarium.
Calcium, alkalinity and other trace elements which are consumed by corals are replaced through water changes (using natural seawater or a quality synthetic salt mix) or the use of a calcium reactor, kalkwasser (calcium water – calcium hydroxide mixed with pure water) or a balanced two-part solution.