The chemistry of the surrounding seawater varies little from one coral reef to the next. Therefore, only one set of parameters is needed for all saltwater aquariums that display reef fishes and invertebrates. Some authors recommend maintaining the temperature at a slightly higher range than recommended here.

Beneficial nitrifying bacteria will have matured completely, and biofiltration will be adequate to permit fish to be stocked at full capacity indefinitely. Though biofiltration is a totally natural process, most aquariums are outfitted with some kind of filtration system. Designed to maximize biofiltration capacity, aquarium filtration equipment may employ a variety of techniques to increase the surface area available for colonization by nitrifiers.

The bacteria refuse to carry out the desired chemical transformations when they float freely; they need to be stuck to a solid surface. Thus we have rotating “bio-wheel” devices, “wet/dry” systems, and “fluidized bed” technology. All these filtration methods provide extremely efficient biofiltration, converting all the ammonia generated within the tank to nitrate in a short period of time.

Aquarium system design sometimes focuses on biofiltration to the exclusion of other important factors because the aquarist is often seen as trying to squeeze the maximum number of fish into the minimum number of gallons. Although you could buy a highly efficient filter system and have the tank teeming with fish, you would be inviting disaster, nearly guaranteeing it, because you would exceed what I like to call the true carrying capacity of the system.

We can debate all day about carrying capacity; that is, how many fish of what size a particular aquarium can support. If by support we simply mean “adequately detoxifying the ammonia waste produced,” we can bump up the number of fish to high population densities indeed. Consider how many fish might be packed into a dealer’s inventory system, for a case in point. Ten saltwater fish in a fifty-gallon tank would not be considered unusual. For the home aquarium display, biofiltration is not the whole story. We must think about the long term success of an aquarium whose residents will be there for the rest of their lives. Fish and other organisms need what I like to call ecological space.

A given species may need swimming room, a minimum number of companions of its own species, or a certain amount of water movement to really thrive. The ability of the aquarium to provide for these needs as well as for basic waste removal is a measure of the true carrying capacity. Taking into account not only waste removal, but also the need for ample oxygen, swimming room, and benign social interactions, ecological space must be allotted in the process of designing the aquarium. Care must be taken not to exceed the true carrying capacity of the system.

The most important physical and chemical cycles operating within the saltwater aquarium are biological filtration, gas exchange, and the day/night cycle. Without biological filtration, an aquarium requires water changes so frequently as to be impractical. Life in an aquarium cannot exist without the exchange of oxygen and carbon dioxide at the surface. Photosynthetic organisms require both light and darkness for their survival, and the alternation of light and dark regulates the metabolism of both fish and invertebrates. Good aquarium design and regular maintenance take care of all these requirements.

Biological Filtration
Fish excrete their wastes directly into the water. Under natural conditions, fish population density, considering the total volume of water surrounding a coral reef, is much lower than that of even the largest aquarium. Dilution, therefore, immediately counters fish waste pollution in the ocean. Additionally, in a short time natural processes degrade the wastes into simple compounds that can be taken up by algae or utilized in some other ecological process.

When we establish an aquarium’s artificial ecosystem, we must harness these same natural processes to promote the survival of our fish and invertebrate display. The totality of these processes as they occur in an aquarium is biological filtration. Biological filtration is the detoxification of wastes by beneficial bacteria known as nitrifiers or nitrifying bacteria. Coating every available surface that lies in contact with oxygenated water, these organisms chemically convert ammonia (the primary component of fish waste) into nitrate (a relatively harmless compound taken up by photosynthesizers).

Biological filtration, or biofiltration, readily develops in the aquarium. All that is required is an ammonia source (fish) and the right kinds of bacteria. The latter are automatically transferred along with fish or any other item taken from the reef or from a previously established saltwater aquarium (the dealer’s inventory system, for example). Within a month, nitrifying bacteria will colonize the aquarium system sufficiently to process a moderate amount of waste.

The gradual development of biofiltration capacity prompts the widely offered recommendation always to stock the aquarium slowly, over a period of several months. Within six months to a year, the population of the system.