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 filte ...

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 colonies of coral polyps held together by calcium carbonate. Most coral reefs are built from stony corals, whose polyps cluster in group ...

system. This method relies on the use of ample

live rock Live rock is rock (geology), rock from the ocean that has been introduced into a marine aquarium, saltwater aquarium. Along with live sand, it confers to the closed marine system multiple benefits desired by the saltwater aquarium fishkeeping, hob ...

(rock with live marine organisms and bacteria on or in it). The theory is that aerobic

bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...

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

ammonia Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...

(from fish and invertebrate waste) into

nitrites The nitrite polyatomic ion, ion has the chemical formula . Nitrite (mostly sodium nitrite) is widely used throughout chemical and pharmaceutical industries. The nitrite anion is a pervasive intermediate in the nitrogen cycle in nature. The name ...

, 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 insol ...

, 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 p ...

, 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: *Adhesive#Anaerobic, Anaerobic ad ...

to free

nitrogen Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...

gas. Left over

are removed through regular partial water changes, or with algal filtration such as an

algae scrubber An algae scrubber is a water filtering device which uses light to grow algae; in this process, undesirable chemicals are removed from the water. Algae scrubbers allow hobbyists to operate their saltwater or freshwater tanks or ponds using nat ...

. 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, public aquariums, and ...

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 language, 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 associat ...

is to use from 1-2 lb (0.45 to 0.9 kg) of

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

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 A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...

invertebrates Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordate subphylum ...

and

coral Corals are colonial marine invertebrates within the subphylum Anthozoa of the phylum Cnidaria. They typically form compact Colony (biology), colonies of many identical individual polyp (zoology), polyps. Coral species include the important Coral ...

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, 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