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 a three U.S. gallon tank (11 L) causes dramatic changes in the system, while the death of that same fish in a 100 U.S. gallon (400 L) 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 or via an air pump. 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, on a daily basis.^[45] 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 20% of the water while cleaning the gravel, or other substrate if the aquarium has one. A good habit is to replace the water extracted while "vacuuming" the gravel as this will eliminate uneaten foods and other residues that settle on the substrate.^[46] Tap water is not considered to be safe for fish to live in because it contains chemicals that harm the fish, so any tap water used must be treated with a suitable water conditioner, such as a product which removes chlorine and chloramine, and neutralises any heavy metals present. The water parameters must be checked both in the tank and in the replacing water, to make sure they are suitable for the species of fish kept.

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 typically 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.^[47] Dissolved organic content and dissolved gases content are also important factors.

A typical home 10 gallon tropical freshwater aquarium

Home aquarists typically use tap water supplied through their local water supply network to fill their tanks. Straight tap water cannot be used in countries 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.^[47] However, chloramine is now used more often and does not leave the water as readily. Additives 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.
More sophisticated 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.^[47] Some aquarists filter or purify their water through deionization or reverse osmosis prior to using it. In contrast, public aquaria with large water needs often locate themselves near a natural water source (such as a river, lake, or ocean) to reduce the level of treatment.
Water temperature determines the two most basic aquarium classifications: tropical vs. cold water. Most fish and plant species tolerate only a limited temperature range: Tropical aquaria, with an average temperature of about 25 °C (77 °F), are much more common. Cold water aquaria are for fish that are better suited to a cooler environment. More important than the range is consistency; most organisms are not accustomed to sudden changes in temperatures, which can cause shock and lead to disease.^[47] Water temperature can be regulated with a thermostat and heater (or cooler).
Water movement can also be important in simulating a natural ecosystem. Aquarists may prefer anything from still water up to swift currents, depending on the aquarium's inhabitants. Water movement can be controlled via aeration from air pumps, powerheads, and careful design of internal water flow (such as location of filtration system points of inflow and outflow).

Nitrogen cycle

The nitrogen cycle in an aquarium

Main article: Nitrogen cycle

Of primary concern to the aquarist is management of the waste produced by an aquarium's inhabitants. Fish, invertebrates, fungi, and some bacteria excrete nitrogen waste in the form of ammonia (which converts to ammonium, in acidic water) and must then pass through the nitrogen cycle. Ammonia is also produced through the decomposition of plant and animal matter, including fecal matter and other detritus. Nitrogen waste products become toxic to fish and other aquarium inhabitants at high concentrations.^[47]

The process

A well-balanced tank contains organisms that are able to metabolize the waste products of other aquarium residents. This process is known in the aquarium hobby as the nitrogen cycle. Bacteria known as nitrifiers (genus Nitrosomonas) metabolize nitrogen waste. Nitrifying bacteria capture ammonia from the water and metabolize it to produce nitrite.^{[citation needed]} Nitrite is toxic to fish in high concentrations. Another type of bacteria, genus Nitrospira, converts nitrite into nitrate, a less toxic substance. (Nitrobacter bacteria were previously believed to fill this role.^{[citation needed]} While biologically they could theoretically fill the same niche as Nitrospira, it has recently been found that Nitrobacter are not present in detectable levels in established aquaria, while Nitrospira are plentiful.)^{[citation needed]} Commercial products sold as kits to "jump start" the nitrogen cycle, often still contain Nitrobacter.^{[citation needed]}
In addition to bacteria, aquatic plants also eliminate nitrogen waste by metabolizing ammonia and nitrate. When plants metabolize nitrogen compounds, they remove nitrogen from the water by using it to build biomass that decays more slowly than ammonia-driven plankton already dissolved in the water.

Maintaining the nitrogen cycle

What hobbyists call the nitrogen cycle is only a portion of the complete cycle: nitrogen must be added to the system (usually through food provided to the tank inhabitants), and nitrates accumulate in the water at the end of the process, or become bound in the biomass of plants. The aquarium keeper must remove water once nitrate concentrations grow, or remove plants which have grown from the nitrates.
Hobbyist aquaria often do not have sufficient bacteria populations to adequately denitrify waste. This problem is most often addressed through two filtration solutions: Activated carbon filters absorb nitrogen compounds and other toxins, while biological filters provide a medium designed to enhance bacterial colonization. Activated carbon and other substances, such as ammonia absorbing resins, stop working when their pores fill, so these components have to be replaced regularly.
New aquaria often have problems associated with the nitrogen cycle due to insufficient beneficial bacteria.^[48] Therefore fresh water has to be matured before stocking them with fish. There are three basic approaches to this: the "fishless cycle", the "silent cycle" and "slow growth".
In a fishless cycle, small amounts of ammonia are added to an unpopulated tank to feed the bacteria. During this process, ammonia, nitrite, and nitrate levels are tested to monitor progress. The "silent" cycle is basically nothing more than densely stocking the aquarium with fast-growing aquatic plants and relying on them to consume the nitrogen, allowing the necessary bacterial populations time to develop. According to anecdotal reports, the plants can consume nitrogenous waste so efficiently that ammonia and nitrite level spikes seen in more traditional cycling methods are greatly reduced or disappear. "Slow growth" entails slowly increasing the population of fish over a period of 6 to 8 weeks, giving bacteria colonies time to grow and stabilize with the increase in fish waste.
The largest bacterial populations are found in the filter; efficient filtration is vital. Sometimes, a vigorous cleaning of the filter is enough to seriously disturb the biological balance of an aquarium. Therefore, it is recommended to rinse mechanical filters in an outside bucket of aquarium water to dislodge organic materials that contribute to nitrate problems, while preserving bacteria populations. Another safe practice consists of cleaning only half of the filter media during each service.

[edit] Aquarium supplies

A way to keep the aquarium clean and fresh is by using specific aquarium cleaning supplies. These may include cleaning agents especially designed to clean the water and keep it fresh, nets, algae magnets and scrapers, algae pads, brushes, gravel cleaners, sealant and tongs and grabbers. A properly cleaned aquarium means healthy and happy fish. Aquarium cleaning must be performed on a regular basis to ensure that the fish are healthy. Also, by maintaining a clean aquarium one makes sure the tank looks appealing to the visitors.
Nets are very important cleaning supplies because they are helpful in transferring the fish to breeders or refugiums or to take them out of the aquarium whenever a thorough cleaning is needed.^[49] Nets come in a variety of sizes and designs. The size one needs depends on the size of the tank they need to clean.
The cleaning liquid agents are substances especially designed to clean the water without harming the health of the fish. Cleaning agents also include scratch removers, lime dissolvers, glass and acrylic polishers, wipes, salt creep removers and magnetic cleaners. All of these are intended to be used on the tank, ornaments and equipment.
Aquarium pest control products may be needed for cleaning aquaria with corals or live rocks. Aquarium pest control is helpful in fighting infestations with different organism coming from new fish or from the plants, corals or rocks that are recently acquired. If not taken care of, infestations like this may cause damage to the aquarium by depleting resources and causing illness.^[50]
The water cleaners are amongst the first aquarium cleaning supplies that must be purchased.^[51] Aquarium water conditioners and additives like chlorine removers and stress relievers make tap water safe for use in aquariums, and should be used when preparing for tank setup or water changes.^[52] The "new tank syndrome" may be avoided if using cycle aids to establish the nitrogen cycle. Also, creating the natural water conditions for an aquarium implies getting aquarium salt, vitamins and supplements.
The level of ammonia in the water must be closely monitored as a too high level of ammonia in the water may cause the death of the fish. The market provides especially designed ammonia removers which transform ammonia into a non-toxic form until the filter is able to process it. Aquarists are recommended to have ammonia removers around for immediate use in case of ammonia emergency.
Water clarifiers are used to clean up the water that might get foamy or cloudy due to chemicals or biological blooms. Overfeeding or fish death can lead to a sudden increase in organic waste which may result in biological clouding. Water clarifiers are useful in these cases. However, they should not be needed too often because excessive clouding can mean that the filters or filter media are not working properly and should be changed.
Excessive algae and cyanobacteria can be removed with the help of algaecides. Although algaecides are the fastest way to solve problems caused by algae they are not recommended in reefs, planted tanks or in those with crustaceans or livebearers. Algaecides are also not a long term solution for this type of issue and aquarists are advised to avoid direct sunlight or lights that are not intended for aquariums on their tanks because they cause algae blooms.
The cleaning supplies that are fluid such as the water purifiers or conditioners are not to replace the thorough cleaning that should be performed at least once in two weeks. However, they are handy supplies to keep the fish healthy until the aquarist can find the right time to perform such a cleaning.

Biological loading

Small aquarium (19 liter) with Paracheirodon innesi, Trigonostigma heteromorpha, and Hemigrammus erythrozonus

Biological load is a measure of the burden placed on the aquarium ecosystem by its inhabitants. High biological loading presents a more complicated tank ecology, which in turn means that equilibrium is easier to upset. Several fundamental constraints on biological loading depend on aquarium size. The water's surface area limits oxygen intake. The bacteria population depends on the physical space they have available to colonize. Physically, only a limited size and number of plants and animals can fit into an aquarium while still providing room for movement. Biologically, biological loading refers to the rate of biological decay in proportion to tank volume.

Calculating capacity

Limiting factors include the oxygen availability and filtration processing. Aquarists have rules of thumb to estimate the number of fish that can be kept in an aquarium. The examples below are for small freshwater fish; larger freshwater fishes and most marine fishes need much more generous allowances.

• 3 cm of adult fish length per 4 litres of water (i.e., a 6 cm-long fish would need about 8 litres of water).^[53]
• 1 cm of adult fish length per 30 square centimetres of surface area.^[54]
• 1 inch of adult fish length per gallon of water.^[53]
• 1 inch of adult fish length per 12 square inches of surface area.^[54]

Experienced aquarists warn against applying these rules too strictly because they do not consider other important issues such as growth rate, activity level, social behaviour, surface area of plant life, and so on.^[55] Establishing maximum capacity is often a matter of slowly adding fish and monitoring water quality over time, following a trial and error approach.

Other factors affecting capacity

One variable is differences between fish. Smaller fish consume more oxygen per gram of body weight than larger fish. Labyrinth fish can breathe atmospheric oxygen and do not need as much surface area (however, some of these fish are territorial, and do not appreciate crowding). Barbs also require more surface area than tetras of comparable size.^[47]
Oxygen exchange at the surface is an important constraint, and thus the surface area of the aquarium matters. Some aquarists claim that a deeper aquarium holds no more fish than a shallower aquarium with the same surface area. The capacity can be improved by surface movement and water circulation such as through aeration, which not only improves oxygen exchange, but also waste decomposition rates.^[47]
Waste density is another variable. Decomposition in solution consumes oxygen. Oxygen dissolves less readily in warmer water; this is a double-edged sword since warmer temperatures make fish more active, so they consume more oxygen.^[47]
In addition to bioload/chemical considerations, aquarists also consider the mutual compatibility of the fish. For instance, predatory fish are usually not kept with small, passive species, and territorial fish are often unsuitable tankmates for shoaling species. Furthermore, fish tend to fare better if given tanks conducive to their size. That is, large fish need large tanks and small fish can do well in smaller tanks. Lastly, the tank can become overcrowded without being overstocked. In other words, the aquarium can be suitable with regard to filtration capacity, oxygen load, and water, yet still be so crowded that the inhabitants are uncomfortable.^[56]