Aquarium Glossary


The process in which the water an organism comes in is balanced to the water in the display tank the organism will be going into.

Water measuring below neutral pH (1.0-6.9).

Swelling at the tip of a tentacle that is full of nematocysts.

Requires the presence of oxygen to live.

Aerobic Bacteria
Bacteria that requires oxygen to survive.

Pertains to corals that do not have zooxanthellae, generally non-reef building coral.

Simple rootless plants that grow in bodies of water in relative proportion to the amount of nutrients available. Algae produce oxygen (photosynthesize) with sunlight (natural or artificial) and use oxygen (respire) during the night hours. Some types of algae are beneficial to aquatic environments while others can be considered a nuisance.

Water tested that is measuring above a neutral pH (7.1-14.0).

The capacity of a system to resist a downward change in pH. Also referred to as carbonate hardness. The recommended range is 8-10 dkh.

A compound of Nitrogen and Hydrogen, formed in the anaerobic decomposition of organic matter. Ammonia can also be added to public water sources to bond with chlorine to form chloramines.

The stunting of growth or inhibition of growth of aquatic animals by means of chemical warfare. This occurs in aquariums between competing animals of the same or different species.

Anaerobic Bacteria
Bacteria that survives in conditions void of oxygen.

The arranging or decorating of an aquarium with ornaments and rocks such as plants (live or plastic), driftwood, ceramic decorations and rock.

A calcium based sand or substrate used in saltwater aquariums.

Also known as brine shrimp. They are small crustaceans that live in brine or brackish water. Artemia nauplii, or baby brine shrimp are used mainly for rearing fry. Adult brine shrimp are used for feeding fish. Artemis is available live, frozen and freeze dried.

Having no sexual organs, being neither male nor female.

The spontaneous casting off of a limb or other body part. Normally occurring when an organism is injured or under attack.

An organism capable of synthesizing (making) its own food from inorganic substances. These organisms use light or chemical energy.


Referring to micro-organisms found in aquariums and ponds, some are beneficial such as Nitrosamines and Nitrobacteria in breaking down fish wastes from toxic ammonium into nitrite into less harmful nitrate. Other bacteria are harmful and act as pathogens attacking primarily weakened fish and causing diseases.

Relating to the bottom under a body of water (the seafloor or bottom of a lake for example) where flora and fauna are found.

Berlin System
The method of maintaining a reef tank with live rock and a protein skimmer as the only filtration techniques employed.

A biological media typically used in many wet/dry type filters. Generally made of plastic in a spherical shape with a large surface for beneficial bacteria to colonize.

Biological Filtration
The use of media to grow colonies of aerobic or anaerobic bacteria to facilitate the removal of dissolved waste in the form of ammonia and nitrite and conversion to nitrate.

Animals and microbes that are able to produce their own light. An example would be squid changing color, or copepods changing color to thwart potential predators.

Refers to the total mass of living matter within a specified area. Also sometimes referred to as bioload.

Refers to a filter that contains both mechanical and biological filtration all in one unit, or at least has the option to portray both capabilities.

The process in which zooxanthellae expel themselves from the tissue of the corals they are living in causing a lack of pigmentation in the coral. Usually associated with high water temperatures or because of excessive lighting.

A pink to reddish cast on the fins and tail of a fish indicating stress, often caused by ammonia or nitrite poisoning.

Polychaete worms that primarily consuming detritus. Once thought to be harmful to reef aquariums, most now believe they are beneficial to a reef tank.

A from of asexual reproduction where an organism creates a new individual from an outgrowth capable of surviving on its own.

The ability of water to resist changes in pH. Also, used to describe situations when additives are placed into the aquarium.


Formed from calcium.

Impregnation with calcium or calcium salts.

A major trace element found in natural and synthetic seawater. Corals in reef tanks will utilize calcium to build their skeletons. Calcium needs to be replenished in a closed system (Aquarium).

Carbon (Activated)
A chemical filter media used to adsorb odors, dissolved organics, pollutants, medications and discolorations.

A hard outer covering or shell made of bone or chitin, such as the fused dorsal plates of turtles. Another example is the portion of an exoskeleton covering the head and thorax of a crustacean.

Carbonate Hardness
See alkalinity

Water running in limited paths and avoiding most of the filter media due to clogging by particulate matter.

A water-cooling mechanism that utilizes refrigerant to cool aquarium water as it passes through the unit. Mainly used in reef aquariums, Chillers can also be used in freshwater and saltwater fish only (FOWLR) systems.

Animals from the phylum Chordata having at some stage of development a dorsal nerve cord and flexible spinal column (notochord).

Circum Tropical
Dealing with areas around tropical or equatorial areas especially waterways.

Phylum that contains hydras, hydroids, jellyfish, sea anemones and corals.

Refers to a symbiotic relationship in which one species benefits while the other is unaffected.

Electronic monitoring devices that have the ability to power on and off other devices. The most popular types of controllers include pH, temperature and Oxidation Reduction Potential (ORP).

Coral like animals from the order zoantharia, commonly called “mushroom corals/anemones” or “false corals.”

Coralline Algae
An encrusting algae that utilizes calcium to grow. This is a desirable algae and growth demonstrates a healthy aquarium. Typically, purple, pink or red in color.

The coral structure or cup formed by an individual polyp in a colony.

The entire coral formed by a colony of polyps.

Hidden, concealed or camouflaged, as in the coloring of an animal.

Cured Live Rock
Live rock that has gone through the curing process (see Curing Live Rock).

Curing Live Rock
The process of removing dead or undesirable organisms that are not able to survive the collecting, handling and shipping of the rock from its collection site to the home aquarium.

A photosynthetic bacterium sometimes referred to as slime algae. Can be seen in a blue green color or red. Generally considered a nuisance “algae.”

Refers to the process of allowing your aquarium or pond water to go through the nitrogen cycle.


Refers to an organism that dwells at or near the bottom of water.

A filter designed to remove unwanted nitrates from an aquarium or pond.  Normally accomplished with a slow flow through media with anaerobic bacteria or via a sulfur-based and aragonite media.

Accumulated waste material such as fish waste or excess food.

Organisms that consume detritus.

A single celled algae normally a brown or golden color that will grow on aquarium walls, decorations and substrate.  

Having digits or finger-like projections.

Organisms that are active during daylight hours.

Abbreviation for Dissolved Organic Compounds.

Drip acclimation:
A method for acclimating newly acquired specimens to their new environment.  Consists of slowly dripping water from the specimen’s new home into the water they arrived. This reduces stress because of the change in water parameters between the new and old water.

Down-flow systems:
Filters in which water enters the top and flows down through media and then exits at the bottom of the system.


En Masse Spawn:
An event where all or mostly all of the local inhabitants are simulated to spawn all at once.

Used to bond rock, plants or corals together.  Most popular types are two part epoxies that harden when mixed together.

The part of the wide lower course of a river where its current is met by the tides of the ocean. Depending on the tides (low and high) this area can go from saltwater to brackish to freshwater.

An organ, such as the siphon on a clam that is used for exhalation.

External Pump:
A pump that operates outside the aquarium or pond, these pumps are generally non-submersible.


In aquarium usage it is to allow an aquarium or pond to run without inhabitants.  Generally, this is done to help kill off any parasites in the aquarium, as there are no hosts for the parasites to live off of.


Filter Feeder:
An animal that strains out particulate matter, including planktonic life forms from the water column to feed upon.

Filtration System (Filter):
A device that will help purify tank or pond water.  The three main components of a filter system will include mechanical (trapping particles), biological (breaking down of waste products such as ammonia and nitrite) and chemical (adsorbing odors and discoloration).

Fish Only System (FO):
Refers to an aquarium system without invertebrates or other organisms contained in the tank, only fish.

Fish Only With Live Rock (FOWLR):
A saltwater aquarium containing fish and live rock.

An asexual reproductive method (Division).

The act of a fish rubbing or scratching their bodies typically to relieve themselves of symptoms associated with parasites or stress.

A chemical that causes particles such a single celled algae and silt to clump together for easier removal.

Formal Ponds: Ponds designed in shapes such as circles, squares and rectangles. Conforming to specific design ideas.

The process of artificial reproduction of corals by breaking, cutting or dividing pieces from the main colony and attaching them to a new base. These pieces eventually become new colonies.  These cuttings are commonly referred to as "frags."

Cuttings of corals from a main colony of coral for the purpose of creating a new colony.  Frags are often traded and sold between reef hobbyists.



A taxonomic category ranking below family and above species.  Generally consisting on a group of species exhibiting similar characteristics.

Glitter Lines (Shimmer Lines):
Light lines viewed underwater on surfaces (such as the sand on the bottom of the ocean) caused by ripples or waves on the surface of that reflect and refract the light from a single source point (i.e. the sun in the wild or a metal halide bulb in an aquarium).

Gravity Fed:
Water flowing into the filter system by the force of gravity and then returned to the aquarium or pond via a pump.

Ground Fault Interrupters (GFI):
It is a device that measures the amperes (number of electrons) traveling through a circuit and quickly opens (breaks) the circuit if there is a small loss or ground fault to prevent you or your livestock from getting shocked.


Head Height:
Calculated in feet, it is the amount of height a pump pushes against gravity through tubing to the highest point of re-entry into the system. This is important to know when determining the correct pump for your water feature.

An electronic device that will heat water to a specific temperature.  Best used with a controller. It is best to replace your heater every 2-3 years.

An organism that eats plant material as its main source of nutrition.

An organism that possesses both male and female sexual organs.

Refers to an organism that cannot synthesize its own food.  It is dependent on complex organic substances for nutrition (heterotrophy).

Horizontal or Cross flow systems:
Water flows through a filter, entering one side, across media and exiting the opposite side of the filter unit.

A device for measuring the salinity or specific gravity of salt water.


A common parasite that fish get especially when stressed.  Visually appear as small salt grains (small white spots) when seen on fish. There are multiple treatment options for this parasite. Generally not deadly to the fish unless it goes untreated.

Aquatic animals that live in the substrate of a body of water, especially in a soft sea bottom (sand or mud substrate).

Informal Ponds:
ponds designed without strict geometric form.

Known as the region between the high tide mark and the low tide mark. Commonly referring to the organisms that dwell in this area.

An animal lacking a backbone or spinal column.


Jaubert System:
Named after Dr. Jean Jaubert.  A filtration system/method used in reef aquariums.  It consists of a deep bed of sand over a buried plastic plate.  Beneath the plate is an area void of sand with a pocket of low oxygenated water known as a plenum. Nitrogenous wastes are broken down as the aquarium water diffuses through the area.


Kalkwasser (Lime Water):
A saturated solution of calcium hydroxide used to raise the calcium levels in a reef tank.  Kalkwasser is available as a powder that is mixed with RO or RO/DI water and dripped into the tank.


A thin scale or plate like structure.  Sometimes used to describe flow (laminar flow). Commonly refers to a unidirectional flow in a flat, horizontal plane.

Abbreviation for Large Polyp Stony coral.

Live Rock:
Rock that has been collected from marine environments used as decoration and filtration in marine fish only and reef tanks.  It will contain micro and macro flora and fauna beneficial to the aquarium.

Live Sand:
Aragonite based sand that has micro and macro organisms living on and in the sand that are beneficial to a marine aquarium.


Refers to alga that is not microscopic. Macroalgae is commonly placed in refugiums in saltwater aquariums.  Some examples include Caulerpa and Chaetomorpha.

The flesh or tissue of mollusks.

Marginal/Emergent Plants:
Plants that grow in or around the edges of the pond. Their leaves and stems rise above the water line and they grow rooted in a submersed soil. Typically their crown is not submerged any more than a couple inches below the water.

Various organisms that spend part of their life cycle as plankton.  Most commonly the plankton state occurs during the larval or egg stages.

Microalgae: Algal forms that are only visible with the use of a microscope.

Electronic devices that are able to read different water parameters such as pH, temperature and ORP.  Monitors differ from controllers because they do not have the ability to turn on or off other devices. Monitors only display the water parameters.

A branch of biology that deals with the form and structure of organisms without the consideration of its function.  Ex. The form and structure of an organism or one of its parts.

Mobile or movable. Moving or having the power to move spontaneously.

An association between two different species of organisms in which each organism benefits.


Nano Plankton: Very small plankton. Composed of organisms measuring from 2 to 20 micrometers.

Necrosis: The process of tissue dying off. Refers to the death of cells or tissues from injury or disease. Also referred to as Rapid Tissue Necrosis (RTN) or Slow Tissue Necrosis (STN).

Nematocysts: A capsule within a specialized cell of certain coelenterates (such as jellyfish) containing barbed, threadlike tube that delivers a paralyzing sting when propelled into attackers and prey. Sometimes also referred to as "stinging cells".

Nitrogen Cycle: A naturally occurring chemical process by which organic wastes in conjunction with wastes from fish are converted by aerobic bacteria to nitrite, and then in turn are converted again by aerobic bacteria to nitrate.

Nitrosamines Bacteria: A specific type of aerobic bacteria that converts ammonia into nitrite.

Nitrospiralis Bacteria: another specific type of aerobic bacteria that converts nitrite to nitrate.

Nori: A type of dried seaweed used to wrap sushi. Also used to feed herbivore fish such as Tangs.


Osculated: Having one or more pairs of eyespots. Theorized as a way to confuse any possible predators.

Octocoral: A member of the phylum Coelenterate (Cnidarians), class Anthozoa characterized by normally having eight tentacles on each polyp.

Oolitic: Rock, usually limestone composed of oolites. A small round calcareous grain found, for example, in limestone.

Operculum: A “platelike” covering over the gills in fishes to help protect the gills.

Order: A taxonomic category of organisms ranking above a family and below a class.

Organic load: A term referring to all animal and plant life in a system. Primarily fish and decomposing organic matter.

Oscula: The “mouthlike” opening in a sponge that is used to expel water. Also referred to as the osculum.

Osmoregulatory System: The system that provides blood to carry oxygen throughout the fishes circulatory system.

Osmosis: Diffusion of fluid through a semi permeable membrane from a solution with a low solute concentration to a solution with a higher solute concentration until there is an equal concentration on both sides of the membrane.

Ostia: A small opening or orifice. Also refers to any of the small openings or pores in a sponge.

Oxidation Reduction Potential (ORP): Measured in millivolts (mV), it is the measure of the ability of the water to break down waste products in the tank. For aquariums the recommended level be between 350-390 mV.


Photosynthetic Active Radiation (PAR): Refers to the readings or light levels and energy given off by a lamp.

pH: The measurement of free hydrogen ions in water measured on a scale from 1.0 (acidic) to 14.0 (alkaline). pH is a contraction that stands for pondus Hydrogenii (weight of hydrogen).

Parasites: Refers to small organisms that use fish as a host organism for survival. Micro-parasites are observed with the use of a microscope and include trichodina, costia, ich, etc. Macro-parasites can be seen by the naked eye and include lice, anchor worm, etc.


Pelagic: Relating to or living in open oceans or seas. Refers to “Ocean going” or "pertaining to the sea".

Photoperiod: The amount of time the daylights are on over an aquarium.

Photosynthesis: The process by which carbon dioxide and water are transformed in the presence of light and chlorophyll into carbon-containing, organic compounds in which oxygen is a by-product.

Photosynthetic: Organisms that use the process of photosynthesis to live and gain energy through utilization of sunlight.

Phylum: A primary division of a kingdom, as of the animal kingdom. Ranking next above a class in size.

Phyto Filtration: the use of plants to remove excess nutrients from the water and aid in particulate settlement; also referred to as vegetative filtration.

Phytoplankton: Free-floating aquatic plants. Microscopic algae suspended in the part of the water column that is penetrated by light.

Pinnules: Lateral branches (feather like or plume like) on the tentacles of a soft coral that give it a feather-like appearance.

Pipe Run: Typically calculated in feet, the amount of pipe that a pump is pushing water through to its eventual destination. Helpful when used in conjunction with head height. This is used to determine the correct pump for your water feature or pond.

Piscine: Fish-Like or fish. Relating to or characteristics of fish or fishes.

Planktivorous: Referring to organisms that feed on plankton.

Planktonic Algae: Single celled, free-floating algae that can make the water appear thick and green like pea soup.

Planulae: The flat, free-swimming ciliated larva of a coelenterate.

Powerhead: A water pump that is submerged inside the aquarium or pond to add extra water movement within the tank or pond.

Predation: The capturing of prey as a means of maintaining life (for nutrition).

Propagation: The process of multiplication or increasing in numbers. This is done by either natural reproduction or fragmentation.

Protein Skimmer (Foam Fractionators): A filter that removes organic waste from a saltwater aquarium. Water and tiny bubbles are mixed within a column. The organic waste is attracted to the bubbles creating foam (skimmate) that flows into a collection cup.

Polyvinyl Chloride (PVC): Hard tubing used for plumbing an aquarium or ponds pumps and/or return water lines.


Quarantine Tank (Hospital Tank): A tank set up separatly from a main or display system used to house new or sick fish livestock. Mainly used to prevent spreading diseases into an established aquarium or pond. Fish should generally be quarantined for a minimum 2-4 weeks before introduction to the main tank or pond.


Radula: A flexible “tonguelike” organ in certain mollusks, having a row of horny teeth on the surface.

Rapid Tissue Necrosis (RTN): Characterized by the rapid loss of tissues on corals generally caused by a pathogen. Generally will result in the sudden death of corals.

Reef Tank (System): A marine aquarium consisting of corals and other invertebrates. Most will also have "reef safe" fish as well. They require high intensity lighting and very exceptional water quality.

Refugium: An area or refuge where microorganisms can live and breed without the worry of predation from fish or other organisms. Also many types of microalgae’s will be kept in the refugium to aid in waste (nitrate and phosphate) removal from the aquarium water.

Regenerate: Refers to the re-growth of a lost appendage or tissue. An example would be a starfish regenerating limbs that have been lost.

Respiration: The process of obtaining energy from organic material, in effect the opposite of photosynthesis, performed by plants during nighttime hours with the by-product carbon dioxide.

Reverse Daylight Photosynthesis (RDP): Term used for running a refugium light opposite of the lights on the main display tank. This process assists in maintaining stable pH in the aquarium.

Reverse Osmosis or Reverse Osmosis Deionization (RO or RO/DI): A filtering unit that purifies tap water for use in aquariums. Using a series of cartridges (sediment, carbon and with deionization) along with a membrane they are able to remove 95 to 99.8% of contaminants found in tap water.

Rhizome: Horizontal underground stems from which roots and shoots develop.


Salinity: Measure of total salts in a given weight of seawater expressed in parts per thousand (ppt). Also see Specific Gravity.

Scute: A horny, chitinous or bony external plate or scale. Also called a scutum.

Sedentary: Refers to animals or organisms that remain or live in one area. Attached to a surface and not moving freely, such as a barnacle.

Sedimentation: The act or process of depositing sediment.

Sepia: Liquid that is exuded by a squid or octopus called "ink." Composed of a highly concentrated solution of the pigment melanin and mucus and tyrosine.

Sessile: Permanently attached or fixed, not free-moving.

Settling tanks: Usually conical in shape. They are used before the bio-filtration unit for aquarium systems and settle out solids with slow-moving water. Typically they are gravity fed units.

Siphon: A tubular organ, where aquatic invertebrates such as squids or clams. Water is taken in and expelled out.

Slough: To shed.

Specific Gravity: The ratio of the density of a given solution to the density of pure water. Natural seawater generally has a SG of 1.025-1.026 on coral reefs.

Spicules: A skeletal element in soft corals (needlelike in appearance) composed of calcium carbonate. Also found in sponges made of silicon dioxide.

Spirulina: A microalgae used in many foods for fish. Has been shown to help boost immunity in fish.

Small Polyp Stony Corals (SPS): Commonly referred to as Hard Corals. Also, Acropora or Montipora Corals.

Subclass: A taxonomic category of related organisms ranking between class and an order.

Submerged Plants: Plants that grow fully underwater.

Substrate: Referring to the layer of stone or sand found on the bottom of an aquatic habitat.

Sump: A low-lying place, such as a pit (or in aquatic terms anything that holds water) that will receive drainage. Berlin sumps traditionally host a protein skimmer, filter socks, bio balls and a return pump.

Surface to Air Ratio: The amount of surface area of pond water not covered by aquatic plants or ice if applicable.

Symbiotic: A close, prolonged association between two or more different organism of different species that may, but does not necessarily, benefit each member (Symbiosis). One of the most famous symbiotic relationships is with a clownfish and anemone.


Tategoi: A Koi that has not reached its full potential a Koi not yet “finished”.

Taxa: Plural of Taxon. A taxonomic category or group, such as phylum, order, family, genus or species.

Taxonomy: The classification of organisms in an ordered system that includes natural relationships.

Trace elements: Minerals needed by plants in small quantities to thrive. Examples would be Calcium, Alkalinity and Magnesium.

Turbidity: Relating to the visibility within a body of water, more turbid water will have more suspended particulates floating in the water column.


Up-Flow System: Water is introduced at the bottom of a filtration unit and then gravity is utilized to allow water to travel up through the media to an exit at the top of the system.


Vascular: Characterized by or containing vessels that carry or circulate fluids. Such as blood, lymph or sap through the body of an animal or plant.


Water Hardness: The concentration of calcium and magnesium salts in the water. Also commonly referred to as Alkalinity.

Water Quality: The chemical balance of water. Usually referred to when discussing levels of ammonia, nitrite, nitrate and pH in a system.


Zooplankton: Plankton that consists of animals, including the corals, rotifers, sea anemones and jellyfish that drift in the water column. Most are microscopic.

Zooxanthellae: Algae that live in a mutually beneficial relationship with invertebrates. They take up waste and carbon dioxide and provide the corals with food (fixed carbon or sugar).