insulation. a popular positioning choice for plywood aquaria is keeping them in a wall. here the use of plywood is hidden by sinking the aquarium inside the wall. putting insulation between the two helps with the insulation of a heated tank. styles a macquarium objects used for aquariums include: coffee tables, sinks, and even toilets. another such example is the macquarium, an aquarium made from the shell of an apple macintosh computer. in recent years, elaborate custom-designed home aquariums costing hundreds of thousands of dollars have become status symbols—according to the new york times, "among people of means, a dazzling aquarium is one of the last surefire ways to impress their peers." kreisel a typical kreisel tank housing several moon jellyfish a kreisel tank (kreisel being german for "spinning top" or "gyroscope") is an aquarium shaped like a horizontal cylinder that is designed to hold delicate animals such as jellyfish and newborn seahorses. these aquariums provide slow, circular water flow with a bare minimum of interior hardware to prevent the inhabitants from becoming injured by pumps or the tank itself. the tank has no sharp angles around its sides and keeps the housed animals away from plumbing. water moving into the tank gives a gentle flow that keeps the inhabitants suspended. water leaves the tank through a screen which prevents animals from being drawn into the pump intake or overflow line. there are several types of kreisel tanks. in a true kreisel, a circular tank has a circular, submerged lid. pseudokreisels are "u" or semicircle shaped, usually without a lid. stretch kreisels are a "double gyre" kreisel design, where the tank length is at least twice the height. using two downwelling inlets on both sides of the tank lets gravity create two gyres in the tank. a single downwelling inlet may be used in the middle as well. the top of a stretch kreisel may be open or closed with a lid. there may also be screens about midway down the sides of the tank, or at the top on the sides. it is possible to combine these designs; a circular shaped tank is used without a lid or cover, and the surface of the water acts as the continuation of circular flow. biotope another popular setup is the biotope aquarium. a biotope aquarium is a recreation of a specific natural environment. some of the most popular biotopes are the freshwater habitats of the amazon and rio negro rivers, the african rift lake environments of lake malawi and lake tanganyika, and saltwater coral reefs of australia, the red sea, and the caribbean sea. the fish, plants, substrate, rocks, wood, coral, and any other component of the display should completely match that of the local natural environment. it can be a challenge to recreate such environments, and most "true" biotopes will only have a few (if not only one) species of fish and invertebrates. finally, an emerging concept for the home is that of a wall mounted aquarium, some of which are displayed at the living art marine center. aquarium size and volume a 1,200,000-litre (320,000 us gal; 260,000 imp gal) aquarium at monterey bay aquarium in california, displaying a kelp forest ecosystem an aquarium can range from a small glass bowl containing less than 1 litre (2.1 us pt) of water to immense public aquaria that house entire ecosystems such as kelp forests. relatively large home aquaria resist rapid fluctuations of temperature and ph, allowing for greater system stability. beginner aquarists are advised to consider larger tanks to begin with, as controlling water parameters in smaller tanks can prove difficult. small, unfiltered bowl-shaped aquaria are now widely regarded as unsuitable for most fish. in order to keep water conditions at suitable levels, aquariums should contain at least two forms of filtration: biological and mechanical. chemical filtration should also be considered under some circumstances for optimum water quality. chemical filtration is frequently achieved via activated carbon, to filter medications, tannins, and/or other known impurities from the water. reef aquaria under 100 litres (26 us gal; 22 imp gal) have a special place in the aquarium hobby; these aquaria, termed nano reefs (when used in reefkeeping), have a small water volume, under 40 litres (11 us gal; 9 imp gal). tunnel at the georgia aquarium, usa practical limitations, most notably the weight of water (1 kilogram per litre (8.345 lb/u.s. gal; 10.022 lb/imp gal)) and internal water pressure (requiring thick glass siding) of a large aquarium, restrict most home aquaria to a maximum of around 1 cubic metre in volume (1000 l, weighing 1,000 kg or 2,200 lb). some aquarists, however, have constructed aquaria of many thousands of litres. public aquariums and oceanariums designed for exhibition of large species or environments can be dramatically larger than any home aquarium. the georgia aquarium, for example, features an individual aquarium of 6,300,000 us gallons (24,000,000 l). nano aquariums a new trend is to have very small aquariums, termed mini aquariums (less than 150 litres or 40 gallons) or nano aquariums (less than 75 litres or 20 gallons). these can be either freshwater or saltwater, and are intended to display a tiny but self-contained ecosystem. components filtration system in a typical aquarium: (1) intake, (2) mechanical filtration, (3) chemical filtration, (4) biological filtration medium, (5) outflow to tank the typical hobbyist aquarium includes a filtration system, an artificial lighting system, an air diffuser and pump, and a heater or chiller depending on the aquarium's inhabitants. many aquaria incorporate a hood, containing the lights, to decrease evaporation and prevent fish from leaving the aquarium (and anything else from entering the aquarium). combined biological and mechanical aquarium filtration systems are common. these either convert ammonia to nitrate (removing nitrogen at the expense of aquatic plants), or to sometimes remove phosphate. filter media can house microbes that mediate nitrification. filtration systems are sometimes the most complex component of home aquaria. aquarium heaters combine a heating element with a thermostat, allowing the aquarist to regulate water temperature at a level above that of the surrounding air, whereas coolers and chillers (refrigeration devices) are for use anywhere, such as cold water aquaria, where the ambient room temperature is above the desired tank temperature. thermometers used include glass alcohol thermometers, adhesive external plastic strip thermometers, and battery-powered lcd thermometers. in addition, some aquarists use air pumps attached to airstones or water pumps to increase water circulation and supply adequate gas exchange at the water surface. wave-making devices have also been constructed to provide wave action. fishes, multicolored pebbles and artificial plants within a home aquarium. an aquarium's physical characteristics form another aspect of aquarium design. size, lighting conditions, density of floating and rooted plants, placement of bog-wood, creation of caves or overhangs, type of substrate, and other factors (including an aquarium's positioning within a room) can all affect the behavior and survival of tank inhabitants. an aquarium can be placed on an aquarium stand. because of the weight of the aquarium, a stand must be strong as well as level. a tank that is not level may distort, leak, or crack. these are often built with cabinets to allow storage, available in many styles to match room decor. simple metal tank stands are also available. most aquaria should be placed on polystyrene to cushion any irregularities on the underlying surface or the bottom of the tank itself that may cause cracks. however, some tanks have an underframe making this unnecessary. another important consideration for aquariums is their electrical usage. water is expensive to keep heated, along with the lights that many aquariums, especially those with live plants have. new aquarists should also pay close attention to their electrical setup for their aquarium, taking care to setup power connections with drip loops to prevent water from getting to outlets. aquarium maintenance large volumes of water enable more stability in a tank by diluting effects from death or contamination events that push an aquarium away from equilibrium. the bigger the tank, the easier such a systemic shock is to absorb, because the effects of that event are diluted. for example, the death of the only fish in an 11-litre (3 us gal; 2 imp gal) tank causes dramatic changes in the system, while the death of that same fish in a 400-litre (110 us gal; 88 imp gal) tank with many other fish in it represents only a minor change. for this reason, hobbyists often favor larger tanks, as they require less attention. several nutrient cycles are important in the aquarium. dissolved oxygen enters the system at the surface water-air interface. similarly, carbon dioxide escapes the system into the air. the phosphate cycle is an important, although often overlooked, nutrient cycle. sulfur, iron, and micronutrients also cycle through the system, entering as food and exiting as waste. appropriate handling of the nitrogen cycle, along with supplying an adequately balanced food supply and considered biological loading, is enough to keep these other nutrient cycles in approximate equilibrium. an aquarium must be maintained regularly to ensure that the fish are kept healthy. daily maintenance consists of checking the fish for signs of stress and disease. also, aquarists must make sure that the water has a good quality and it is not cloudy or foamy and the temperature of the water is appropriate for the particular species of fish that live in the aquarium. typical weekly maintenance includes changing around 10–30% or more of the water while cleaning the gravel, or other substrate if the aquarium has one; however some manage to avoid this entirely by keeping it somewhat self-sufficient. a good habit is to remove the water being replaced by "vacuuming" the gravel with suitable implements, as this will eliminate uneaten foods and other residues that settle on the substrate. in many areas tap water is not considered to be safe for fish to live in because it contains chemicals that harm the fish. tap water from those areas must be treated with a suitable water conditioner, such as a product which removes chlorine and chloramine and neutralizes any heavy metals present. the water conditions must be checked both in the tank and in the replacement water, to make sure they are suitable for the species. water conditions the solute content of water is perhaps the most important aspect of water conditions, as total dissolved solids and other constituents dramatically impact basic water chemistry, and therefore how organisms interact with their environment. salt content, or salinity, is the most basic measure of water conditions. an aquarium may have freshwater (salinity below 500 parts per million), simulating a lake or river environment; brackish water (a salt level of 500 to 30,000 ppm), simulating environments lying between fresh and salt, such as estuaries; and salt water or seawater (a salt level of 30,000 to 40,000 ppm), simulating an ocean environment. rarely, higher salt concentrations are maintained in specialized tanks for raising brine organisms. saltwater is usually alkaline, while the ph (alkalinity or acidicity) of fresh water varies more. hardness measures overall dissolved mineral content; hard or soft water may be preferred. hard water is usually alkaline, while soft water is usually neutral to acidic. dissolved organic content and dissolved gases content are also important factors. home aquarists typically use tap water supplied through their local water supply network to fill their tanks. straight tap water cannot be used in localities that pipe chlorinated water. in the past, it was possible to "condition" the water by simply letting the water stand for a day or two, which allows the chlorine time to dissipate. however, chloramine is now used more often and does not leave the water as readily. water conditioners formulated to remove chlorine or chloramine are often all that is needed to make the water ready for aquarium use. brackish or saltwater aquaria require the addition of a commercially available mixture of salts and other minerals. this aquarium features a heated tank and a glass-enclosed top for warmth during winter. some aquarists modify water's alkalinity, hardness, or dissolved content of organics and gases, before adding it to their aquaria. this can be accomplished by additives, such as sodium bicarbonate, to raise ph. some aquarists filter or purify their water through deionization or reverse osmosis prior to using it. in contrast, public aquaria with large water