kb/data/en.wikipedia.org/wiki/Aquarium-6.md

title	chunk	source	category	tags	date_saved	instance
Aquarium	7/8	https://en.wikipedia.org/wiki/Aquarium	reference	science, encyclopedia	2026-05-05T09:00:40.028331+00:00	kb-cron

The biological load, or bioload 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. Adding plants to an aquarium will sometimes help greatly with taking up fish waste as plant nutrients. Although an aquarium can be overloaded with fish, an excess of plants is unlikely to cause harm. Decaying plant material, such as decaying plant leaves, can add these nutrients back into the aquarium if not promptly removed. The bioload is processed by the aquarium's biofilter filtration system.

==== 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). 1 cm of adult fish length per 30 square centimetres of surface area. 1 inch of adult fish length per US gallon of water. 1 inch of adult fish length per 12 square inches of surface area. 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, filtration capacity, total biomass of plant life, and so on. It is better to apply the overall mass and size of a fish per gallon of water, than simply the length. This is because fish of different sizes produce quite differing amounts of waste. 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. 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. 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. 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. For planted freshwater aquariums, it is also important to maintain a balance between the duration and quality of light, the amount of plants, CO2 levels and nutrients. Light exposure within the tank environment can also influence nutrient concentrations. For a given amount of light, if there is insufficient number of plants or insufficient CO2 to support the growth of those plants, so as to consume all the nutrients in the tank, the result would be algae growth. While there are fishes and invertebrates that could be introduced in the tank to clean up this algae, the ideal solution would be to find the optimal balance between the above-mentioned factors. Supplemental CO2 can be provided, whose quantity has to be carefully regulated, as too much CO2 may harm the fishes.

== Aquarium classifications ==

From the outdoor ponds and glass jars of antiquity, modern aquaria have evolved into a wide range of specialized systems. Individual aquaria can vary in size from a small bowl large enough for only a single small fish, to the huge public aquaria that can simulate entire marine ecosystems. One way to classify aquaria is by salinity. Freshwater aquaria are the most popular due to their lower cost. More expensive and complex equipment is required to set up and maintain marine aquaria. Marine aquaria frequently feature a diverse range of invertebrates in addition to species of fish. Brackish water aquaria combine elements of both marine and freshwater fishkeeping. Fish kept in brackish water aquaria generally come from habitats with varying salinity, such as mangrove swamps and estuaries. Subtypes exist within these types, such as the reef aquarium, a typically smaller marine aquarium that houses coral. Another classification is by temperature range. Many aquarists choose a tropical aquarium because tropical fish tend to be more colorful. However, the coldwater aquarium is also popular, which includes fish from temperate areas worldwide.