The Berlin Method of biological

filtration Filtration is a physical separation process that separates solid matter and fluid from a mixture using a ''filter medium'' that has a complex structure through which only the fluid can pass. Solid particles that cannot pass through the filter ...

is a method for maintaining a clean and stable environment within a saltwater aquarium, typically a

coral reef A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of Colony (biology), colonies of coral polyp (zoology), polyps held together by calcium carbonate. Most coral reefs are built from stony corals, wh ...

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 Aerobic means "requiring air," in which "air" usually means oxygen. Aerobic may also refer to * Aerobic exercise, prolonged exercise of moderate intensity * Aerobics, a form of aerobic exercise * Aerobic respiration, the aerobic process of cel ...

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...

covering the surface of the porous live rock and sand convert harmful

ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous ...

(from fish and invertebrate waste) into nitrites, then

nitrates Nitrate is a polyatomic ion with the chemical formula . Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are soluble in water. An example of an insolu ...

, which are much less harmful to the tank's inhabitants. Through the process of

diffusion Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical ...

, the

move deep within the rock where they are converted by

anaerobic Anaerobic means "living, active, occurring, or existing in the absence of free oxygen", as opposed to aerobic which means "living, active, or occurring only in the presence of oxygen." Anaerobic may also refer to: * Anaerobic adhesive, a bonding a ...

to free

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...

gas. Left over

are removed through regular partial water changes, or with algal filtration such as an algae scrubber. As an added measure, a

protein skimmer 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. Sm ...

is used to remove some of the dissolved organic compounds before they break down into

, although skimmers do not remove ammonia from fish urea. The typical

rule of thumb In English, the phrase ''rule of thumb'' refers to an approximate method for doing something, based on practical experience rather than theory. This usage of the phrase can be traced back to the 17th century and has been associated with various t ...

is to use from 1-2 lb (0.45 to 0.9 kg) of live rock per gallon (US) (3.7 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 Fish are Aquatic animal, aquatic, craniate, gill-bearing animals that lack Limb (anatomy), limbs with Digit (anatomy), digits. Included in this definition are the living hagfish, lampreys, and Chondrichthyes, cartilaginous and bony fish as we ...

invertebrates Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordat ...

and

coral Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They typically form compact colonies of many identical individual polyps. Coral species include the important reef builders that inhabit tropical oceans and se ...

s use for 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 __NOTOC__ In marine and reef aquariums, a calcium reactor creates a balance of alkalinity. An acidic solution is produced by injecting carbon dioxide into a chamber with salt water and calcium rich media. The carbon dioxide lowers the pH by prod ...

, kalkwasser (calcium water – calcium hydroxide mixed with pure water) or a balanced two-part solution.

References

#http://www.fishchannel.com/fish-fun/fish-terms/fish-definitions/berlin-method.aspx #http://saltaquarium.about.com/od/denitratorunits/fl/What-Is-A-Saltwater-Aquarium-Berlin-Filtration-System.htm #http://www.aquarium-design.com/reeftheory.html {{Aquarium Fishkeeping