AC: AquaClear. Make of filter.

Acid, Acidic: a pH of less than 7.

Acrylic: Plastic material used to construct fish tanks, filters and accessories.

Actinic: Technically, the property of radiant energy, especially in the visible and ultraviolet spectral regions, by which chemical changes are produced. In the aquarium, a type of fluorescent light that emulates the blue colour of the sea below 10 meters.

Activated carbon: A commonly used chemical filter media used to adsorb impurities from the water.

Adipose fin: The small fin located between the dorsal fin and the caudal fin on characins.

Adsorption: The process by which filter media attracts unwanted molecules to its surface.

Aeration: Getting oxygen into the water, usually by disturbing the surface.

Aerobic: Needing oxygen.

Africans: Cichlids from the hard, salty African rift lakes.

Air pump: A pump which moves air. The most common types are diaphragm pumps and cylinder pumps are available.

Airstone: A porous fitting which diffuses air from a pump into smaller bubbles. Usually made of wood or plastic foam.

Algae: Algae are classified as plants, although they share many characteristics with monerans (fungus).

Alkaline: According to Webster, "1 : a soluble salt obtained from the ashes of plants and consisting largely of potassium or sodium carbonate; broadly : a substance (as a hydroxide or carbonate of an alkali metal) having marked basic properties." Also, having a high carbonate hardness or kH. However, it is sometimes erroneously used to mean water having a pH of above 7.

Ammonia (NH3): A dissolved gas produced by the breakdown of organic waste products. It is extremely toxic and caustic and should be below measureable levels in a cycled tank.

Ammonia Tower: A biological filtration system consisting chamber with filter media through which water is run. that promotes bacterial growth. Most commonly referred to as a wet/dry filter.

Amyloodinium: Marine Velvet (parasite). Symptoms can include cloudy eyes, gasping for breath, listlessness, and white spots gold or brown spots, rough skin, and rubbing against rocks, etc. Copper is the usual treatment.

Anabantoids: Freshwater species characterized by an organ in their "forehead" that permits them to breathe atmospheric oxygen. Bettas and gouramis are the most commonly seen anabantoids.

Anaerobic: Literally "without air". Anaerobic bacteria also produce hydrogen sulfide and other undesirable substances in the freshwater aquarium.

Anal fin: Vertical fin below the fish just in front of the caudal fin (tail).

Aragonite: Calcium Carbonate. The substance that makes up the calcium carbonate skeletons of reef coral and some shells.

Anoxic: Relating to or marked by a severe deficiency of oxygen in tissues or organs. Also refers to areas of low oxygen content in aquaria.

Artemia: Brine shrimp.

Asexual reproduction: Reproducing by means other than sex (splitting, fission).

Bacteria: Small single celled organisms from the Moneran kingdom, classified together because they lack nuclear membranes.

Ballast: A transformer providing the power supply for fluorescent and metal halide lighting.

Barbel: Whisker-like projections around the mouth the fish. Usually sensory organs.

Basic: Having a pH of above 7

Benthic: Living on or under the bottom of the ocean.

Berlin Method of Filtration: A biological method of filtration which involves only live rock and a protein skimmer, leaving the aquarium bottom empty of substrate.

Bio-balls: Biological filter media consisting of open plastic balls.

Biological Filtration: The process of passing water over colonies of beneficial bacteria which processes the ammonia secreted by fish and other living things to nitrate.

Biotope: A region uniform in environmental conditions and in its populations of animals and plants. Or, an aquarium, which simulates such a region.

Black Water: Water that has a dark cola-like color caused by Humic acids, it has a very low pH and is very soft, common in the Amazon River basin.

Brackish: Water with salinity between fresh water and seawater. Brackish aquaria have a specific gravity of between 1.002 and 1.008.

Breeding tank: An aquarium set up specifically with the proper parameters for conditioning and breeding.

Brine shrimp: Tiny crustaceans that are commonly used as food for freshwater and marine fish.

Bubble nest: A nest, which is constructed of air bubbles, usually produced by the male. Anabantoids such as bettas and gouramis are the most common bubble nest builders.

Buffer: A substance dissolved in the water to counteract changes in the pH.

CA: Cichlid shorthand for Central America.

CAE: Chinese Algae Eater. Gyrinocheilus aymonieri A cyprinid, which eats algae while young, but as an adult, can get very aggressive and become more omnivorous.

Calcium: A necessary element used by salt-water corals and other organisms for their calcium carbonate skeleton or shell.

Calcium Chloride CaCl2: A form of calcium sometimes added to reef tanks to maintain the calcium level. Calcium hydroxide is preferred.

Calcium Hydroxide Ca(OH)2: Also kalkwasser. The preferred additive to maintain calcium levels in a marine tank with growing corals, clams, and calcareous algae.

Canister Filter: An external filter, which pushes water through a canister containing various filter media.

Carapace: A bony or hard shell that covers part or all of animals such as turtles and crabs.

Carbon Dioxide CO2: A by-product of respiration. Plants require CO2 to photosynthesise, which generates molecular oxygen.

Carbon: See activated carbon.

Carbonate Hardness: A measure of carbonates and bicarbonates dissolved in the water. It is measured in degrees of hardness. Indicates the pH buffering capacity of the water.

Caudal fin: The single fin mounted vertically at the rear of the fish. The tail fin.

Caudal penduncle: The slender section between the caudal fin and the main body of the fish.

Characin: Fish with a scaled body but no scales on the head and an adipose fin. Most are schooling fish and are usually active during the day with a short dorsal fin and a deeply cleft caudal fin. They come from South and Central America and Africa.

Chemical Filtration: Passing the water through a medium, which adsorbs certain substances in the water.

Chiller: A device, which makes aquarium water cooler.

Chloramines: Used as a bactericide in an increasing number of municipal water supplies. A combination of ammonia and chlorine, it is very stable and it does not outgas from the water as chlorine does. Lethal to aquatic animals and biological filtration.

Chlorine: Also used as a bactericide in municipal water supplies. Extremely toxic, it can be removed with water conditioner or by out gassing (letting the water sit for 24 hours).

Cichlid: A large family of fish made up of a variety of species. Characterized by dual nostrils and their level of parental care. Cichlidae.

Cirri: Short, stubby organs located above the eyes of some cold water species.

Commensal: A relationship where two or more different kinds of animals live together and one benefits while the other is unaffected.

Community: Different species of fish kept in the same aquarium.

Conspecific: The same species.

Controller: A device, which measures some parameter of an aquarium, and then switches on and off another device to affect the aquarium. Typical controllers include redox, and pH.

CRI: Colour rendering index. A number used for rating light bulbs on their ability to accurately reproduce color on scale up to 100, where 100 is equal to sunlight.

Crushed coral: A Calcareous substrate material with pH buffering abilities, for marine aquaria.

Cyanobacteria: Commonly referred to as "red slime algae" in marine aquaria and "blue-green algae" in freshwater aquaria. Not an algae at all, but a fast-growing bacteria.

Deioniser: A filter used to purify tap water by passing the water through a combination of ionically charge resins which remove impurities.

Denitrification: Breakdown of nitrates by anaerobic bacteria into other forms.

Detritus: Organic compounds, usually collecting at the bottom of the aquarium.

Detrivores: Animals that eat detritus. Marine detritvores include urchins, starfish and crabs.

dGH: "Degrees of general hardness".

Diatom: Single-celled protists with hard, silica-based shells .

Diatom Filter: Mechanical filters which use diatomaceous earth as a filter medium to remove very fine particles from the water.

Diatomaceous earth: A filter media made up of skeletons of diatoms.

DIY: Do-it-yourself.

dKH: "Degrees of carbonate hardness".

DOC: Dissolved organic compounds.

Dolomite: A limestone gravel which raises both pH and kH of the water.

Dorsal fin: The fin at the top of the body of the fish. Some fish have two, one behind the other.

Dorsal Surface: The top surface of the body of the fish.

Dosing pump: A pump, which serves to supply a specific level of some substance. Can be used to medicate, add trace elements or add water to make up water for evaporation.

Drip loop: Arranging an electrical cord in a "U" shape so that water does not travel along the cord to the electrical outlet.

DSB: Deep sand bed.

Ebo: Ebo Jager aquarium heaters.

Egg layer: Reproduction by a female depositing eggs in a particular place, and the male coming behind to deposit his milt (sperm).

End cap: A water resistant socket for fluorescent lamps.

External Filter: A filtration device, which is kept outside of the aquarium.