Aquarium Terminology

by Cubby on June 25, 2012

Aquarium Terminology / Definitions / Glossary


Actinic Lights – A florescent lighting system which emits a blue spectrum which is required by corals and most reef creatures which contain photosynthetic algae.

Activated Carbon – Carbon to work in conjunction with filtration. It is used to remove toxins from the water but is known to release Phosphate in to the aquarium once the media is exhausted.

Adipose Fin – The small fin located between the dorsal fin and caudal fin.

Air Pump – Pumps air through airline to an air stone or something similar.

Algae – A growth that can resemble plants but is far from the case, normally caused by poor water conditions, aquariums in direct sunlight, high Nitrate (NO3) levels and high Phosphate (PO4) levels.

Alkalinity – High Alkalinity will result in a stable pH level, Alkalinity can be raised by using a carbonate buffer.

Ammonia (NH3) – A toxin that builds up in aquariums, the toxin is caused by fish waste and things decaying in the tank. Ammonia in a fish tank is the first stage of the Nitrogen Cycle which is removed by bacteria that converts it to Nitrite (NO2) and then Nitrate (NO3).

Amyloodinium Ocellateum – Commonly known as “Marine Velvet” or “Saltwater Ick”. Signs are cloudy areas around the eyes, gasping for breath and white spots.

Anaerobic – Areas of the aquarium where no oxygen is present such as live rock or under the substrate. Anaerobic bacterial uses these areas to convert Nitrate (NO3) in to Nitrogen gas.

Anal Fin – A single vertical fin which is located on the under side of the fish.

Aragonite – A mineral containing Calcium found in rock, gravel or sand.

Artemia – Is another term that brine shrimp are known as.

Asexual Reproduction – No sex or sex organs meaning reproduction would be done by other means.

Auto Top Up – A device that is able to sense when your water level drops below a certain level then top the aquarium water up from a container it’s connected to by tubing.

Ballast – The power source for aquarium lighting.

Base Rock – Normal rock not live used to bulk up the rock work in an aquarium.

Barbels – These are the whisker looking appendages around the mouth area of catfish.

Benthic/Benthos – Something that lives under the substrate at the bottom of the ocean.

Berlin System – Saltwater filtration using live rock and a protein skimmer only.

Biological Filtration – This method of filtration uses bacteria to break down toxins in the water via the Nitrogen Cycle. Some examples of these are under gravel filters, trickle filters and sponge filters.

Bivalve – A shelled animal where their shell is two separate halves connected by a flexible hinge.

Bleaching – When corals expel their colourful zooxanthellae and turn pale or white in colour.

Brackish Water – The middle ground between freshwater and saltwater. This occurs in mouths of rivers near the sea where saltwater fish are moved by currents to brackish water and vice versa. Brackish water is a mixture of saltwater and fresh water.

Brine Shrimp – A tiny shrimp which are also known as “Sea Monkeys” these are sold as fish food.

Buffer – An agent that is added to aquariums to raise Alkalinity and or adjust the Ph level in the water.

Byssus Gland – Found on shelled animals, it’s a means of allowing the animals to attach itself to rocks.

Calcareous – A substance formed of or containing Calcium carbonate which can help keep a stable Ph level.

Calcification – The process of how corals and coralline algae extract calcium from seawater and deposit it in the form of calcium carbonate.

Calcium – A mineral of which corals depend on to be able to grow and form a strong skeleton.

Canister Filter – A mechanical filter which is external to the aquarium, water is sucked out of the aquarium then pumped through the canister which can contain sponges and filter media then returned to the aquarium.

Carapace – A hard shell that covers part of an animal, examples are turtles and crabs.

Carbon – A substance (normally in the form of a sponge) used as part of the filter system to remove excess Nutrients in the water.

Carbon Dioxide – The gas CO2 is a necessary nutrient for plants, and can be used to lower the pH.

Carbon Dosing – A method of dosing your aquarium daily with a carbon source such as Vodka, Sugar, Vinegar and Vitamin C to reduce Nitrate (NO3) and Phosphate (PO4) levels in the water.

Carnivore – Animals which hunt and eat other animals.

Caudal Fin – Commonly known as “Tail fin” a fin which is located at the rear end of the fish.

Caulerpa – A type of algae which grows very rapidly.

Caudal Peduncle – This is the part of the fish that attaches the Caudal (tail fin) to the body of the fish.

Chemical Filtration – Filtration that uses chemical processes to clean and remove toxins from the water.

Cheato – A controllable macro algae to eat up the same nutrients as a result reducing undesirable algae’s.

Chiller – A device used to cool aquarium water, when the water temp reaches a certain level the chiller turns on sucking water in, chilling it then returning it to the aquarium.

Chlorine – Added to water to kill bacteria, Chlorine is toxic to fish so must be removed before the water can be added to the aquarium.

Cnidaria – A collection of invertebrate animals which include Anemones, corals, jellyfish and hydroids.

Coelenterata – An animal which has a central mouth surrounded by tentacles which can sting, examples include anemones, corals and jellyfish.

Coenenchyma – The tissue of a Zoanthid that surrounds the polyps.

Conspecific – Animals of the same species.

Copper – A metal used to cure diseases and parasites in an aquarium. Copper is toxic to invertebrates and should not be used in a reef tank.

Coralline Algae – A type of encrusting algae that forms on rocks and other hard surfaces. Very colourful and sort after by most reef keepers, colours range from red, purple and pink.

Crustaceans – Hard shelled invertebrates such as crabs and shrimps.

Cyano – Short for Cyanobacteria.

Cyanobacteria – Commonly known as “Red slime algae” which is not technically an algae. It is a bacteria which is normally caused by poor water quality and excess nutrients in the water.

Cryptocaryon – A parasitic infection that shows in the form of white spots on the fish body and fins. Cleaner fish and invertebrates can remove the parasite but may not be able to cure the entire tank.

CUC – Clean Up Crew, this term refers to a group of invertebrates that are tank scavengers helping to eat uneaten foods and algae that get in places that fish cannot.

Cycle/Cycling – A term used when an aquarium is still in the stages of its nitrogen cycle.

Diatoms – A single celled organism that forms a brown film on the aquarium glass, substrate and rocks. This normally occurs in an aquarium that is cycling, just finished cycling, has poor water flow, not using RODI water or has excess silicate in the water.

Deionizer – A device used to filter water of its impurities.

Deitrification – The process of Nitrate being converted in to Nitrogen gas.

Detritus – Aquarium waste that has accumulated on the substrate or rocks in piles. Detritus is high in nutrients which can cause Nitrate (NO3) to rise and also cause algae.

Detrivores – Animals that eat detritus.

Dorsal Fin – The fin located on top of the fish, some fish have two dorsal fins.

Dosing Pump – A device used to inject small amounts of chemicals and trace elements in to the aquarium water.

Endemic Species – A species that is normally only found in one area or region.

Filter – A device used to filter aquarium water of debris and unwanted particles.

Filter Feeder – An organism that filters out nutrients in the water such as bacteria and detritus.

Filter Medium – A substance used by the filter to remove waste from the water, examples are sponges and filter floss.

FOWLR – Fish Only With Live Rock, is exactly that. An aquarium that has no corals just fish and live rock.

Frag – Short for Fragment, so a coral frag will be a piece of another coral.

Fuge – Another word used for refugium, see refugium.

Gills – The membranes which the fish absorb dissolved oxygen from the water.

Halogen Lights – A type of light that emits a yellow coloured spectrum.

Heater – A device used to heat the water in an aquarium to the appropriate temp.

Head and Lateral Line Erosion – Commonly known as “Hole in the head disease”. The fish will develop holes in the head and sometimes along its lateral line. Main causes of this are poor water quality, lack of vitamin C and stress.

Herbivore – An animal that eats plants.

Hermatypic – Organisms that contain Zooxanthellae.

Hermaphrodite – An animal which is both a male and female.

Hitchhikers – A term used when live rock is purchased only to find it comes with some form of animal life an example would be buying some rock only to see after putting it in the aquarium a crab roaming around the rock.

HO – High Output, this normally refers to a type of fluorescent tube.

Hydrometer – A device used to measure the salinity of aquarium water.

Invertebrates – Animals with no backbones.

Iodine – A trace element found in seawater which is needed in small quantities for reef invertebrates especially corals.

Kalk – Kalk (Kalkwasser) is used to raise Alkalinity in an aquarium.

Kelvin – Scale used to measure the colour of light a tube emits.

Larvae – This is the first stage a fish/invertebrate goes through after hatching.

Lateral Line – A line of perforated scales which are along the side of a fish that connects to an organ used to sense vibrations in the water.

Live Rock – Rock that has been removed from the ocean which will have a range of critters attached to them which helps the filter of aquarium water through Nitrification.

Livebearer – A fish which gives birth to live young.

LPS – Large Polyped Stony.

Macroalgae – A large plant like algae which can be used to lower Nitrates (NO3) in aquariums.

Mechanical Filtration – A filter which removes waste, debris and unwanted particles from the water. Example mechanical filters are canister filters, under gravel filter and wet/dry filters. Click here to read our filtration guide.

Metal Halide – A type of lighting that uses gas to give off a very bright light. The light these emit are very similar to sunlight and are recommended for reef aquariums.

MH – Metal halide. Click here to read our lighting guide.

Microalgae – Small types of algae such as hair algae.

Mollusks – A group of soft bodied invertebrates such as snails, clams and squids.

Nano Reef/Tank – A name given to a small marine aquarium.

Nitrate (NO3) – Nitrate (NO3) is the final stage of the Nitrogen cycle. Nitrate (NO3) is not toxic but can cause harm in high levels, Nitrate (NO3) can be removed by using biological filtration, water changes and carbon dosing.

Nitrification – The process by which Nitrite (NO2) is converted to Nitrate (NO3).

Nitrobacteria – The bacteria which is live in a biological filtration system that converts Nitrite (NO2) in to Nitrate (NO3).

Nitrogen Cycle – The Nitrogen cycle is the break down of animal waste. Waste will cause ammonia (NH3) which is converted by bacteria to Nitrite (NO2) which is then converted to Nitrate (NO3).

Nitrosomonas – The bacteria which is live in a biological filtration system that converts ammonia (NH3) to Nitrite (NO2).

Octocoral – An Octocoral has eight tentacles on each Polyp.

Omnivore – Animals who eat both vegetables and meat.

Osmolator – A device used to replace evaporated water and maintain a stable water gravity.

Osmosis – The process of water passing through a membrane to remove impurities.

Osmotic Stress – A reaction to drastic changes in the animals water salinity.

Ostracitoxin – A fish poison secreted in to the water by some fish.

Ozone – A very reactive form of oxygen which is used in conjunction with a protein skimmer to maximise skimming.

Ozonizer – A device that uses high voltage electricity to produce ozone.

Parasite – An organism that feeds of tissue of another organism.

Pectoral Fins – The paired pectoral fins are located on each side, usually just behind the operculum.

Pelvic Fins – Paired fins behind or below the pectoral fins

pH – Is the measurement of how acidic or how much alkaline is in your water.

Phosphate (PO4) – A nutrient which in excess fuels most aquarium algae.

Photoperiod – The length of time aquarium lights are on for.

Phytoplankton – Microscopic plants in seawater.

Plankton – Tiny marine animals which are carried by water currents.

Polyp – The living part of a coral.

Powerhead – A small water pump used to create water flow in an aquarium.

Protein Skimmer – A device used to create air bubbles to remove fatty acids and other organic wastes.

Quarantine – A section or separate tank isolated away from your main tank used to keep sick fish.

Reactor – A device used to pass water through before being returned to the aquarium. These can be used with media to remove certain nutrients from the water.

Red Slime Algae – A red slime like substance which forms on aquarium substrate, glass and rocks.

Refugium – A refugium is a separate, smaller tank that’s plumbed into the system. This area is often used for Deep Sand Beds, and for growing Caulerpa for the purpose of nutrient export.

Reverse Flow Filtration – A biological filtration system that returns the water to the tank through the bottom instead of the top.

Reverse Osmosis – A process of filtering water through several membranes to remove impurities.

RO Unit – Reverse Osmosis unit.

RODI Unit – Reverse Osmosis and Deionization unit.

Salinity – The number of dissolved grams of salt in 1,000gr of water.

Saltytank – A term used to refer to a salt water aquarium.

Sessile – An organism that is unable to move about, it will be permanently attached to something like a rock.

Silicone Sealant – An adhesive used to seal the pieces of glass in aquariums.

Skimmer – A shortened version of protein skimmer.

Sponge Filter – A sponge which fits inside either an internal or external filter which is able to do both mechanical and biological filtration.

SPS – Small Polyped Stony.

Strontium – A trace element found in seawater that is needed for corals with calcaregous skeletons to grow.

Substrate – The base of which an organism grows.

Sump – A separate tank located under the display tank used as filtration and to house heaters, reactors and protein skimmers etc.

Sweeper Tentacles – Long string like tentacles used by more aggressive corals to sting nearby corals in order to maintain their territory for growing space.

Siphon – A length of hose that used gravity to move water from a high point to a lower point.

Symbiotic – Where two different organisms live together in a beneficial relationship.

Trace Elements – The necessary elements in a marine aquarium that do not occur as naturally as in the ocean.

Trickle Filters – Biological filters where water is trickled over filter media and exposed to air to help the Nitrification process. Click here to read our filtration guide.

Turnover – The rate of how much water flows within an aquarium.

UGF – Under gravel filter. Click here to read our filtration guide.

ULNS – Ultra Low Nutrient System, is a term used for an aquarium that has very low Nutrient levels via equipment to remove these or by carbon dosing.

Ultraviolet Sterilizer (UV) – A device that sterilises water by passing it through a glass tube around an ultraviolet light.

Under gravel Filter – A filter that works by sucking the water through the gravel then up a tube and back to the top of the aquarium. This provides both mechanical and biological filtration.

Venturi – A valve that produces a mass amount of air bubbles in the water which are used by protein skimmers.

VHO Lights – Very High Output lights are fluorescent lights that give of a very high intensity of light.

Water Change – The process of removing a certain percentage of your aquarium water which removes excess nutrients then replacing the water with fresh.

Wet-dry Filter – A filter where the water is exposed to air to aid the Nitrification process.

Zooplankton – Tiny microscopic animals found drifting in seawater.

Zooxanthellae – Tiny plants that live in a symbiotic relationship with certain corals.

Zoa – Short for Zoanthid which is a type of coral.

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