Glossary of Aquarium Terms

This glossary of aquarium terms contains definitions for some of the most common words used in the hobby.


Acclimate - The process in which one will allow for an inhabitant to move from one water source to another (such as moving from the pet store's tank to your aquarium).

Acidic - Relates to the pH scale in which anything that is measured below a pH of 7.0 is considered an acid (or acidic).

Aeration - Refers to increasing the amount of air that is passed through the water in an aquarium (also known as creating surface agitation to do so).

Aerobic - Requires the presence of oxygen to survive.

Ahermatypic - Relates to corals that do not have zooxanthellae and are generally not reef-building coral.

Algae - A simple non-flowering aquatic plant of a large group that contains chlorophyll but lacks true stems, roots, leaves, and vascular tissue. Some algae can be beneficial while others can be labeled as a nuisance/issue.

Alkaline - Relates to the pH scale in which anything equal to or above a pH of 7.0 is considered a base (or basic/alkaline).

Alkalinity - The capacity of something to resist a downward change in pH (normally referred to as carbonate hardness).

Ammonia - NH3 is a toxic chemical byproduct produced during the breakdown of proteins in uneaten fish food, decaying waste, or excreted by aquatic animals inside of the aquarium.

Anaerobic - Refers to something that can survive in conditions without any oxygen.

Aragonite - A calcium-based material that is used in substrates of aquariums.

Asexual - An organism that has no sexual organs, and therefore is neither male nor female.

Autotrophic - An organism that is capable of synthesizing (creating) its food from inorganic substances.


Bacteria - Refers to microorganisms that are found, some can be beneficial (ex; Nitrosamines and Nitrobacteria in breaking down waste) or harmful (those that act as pathogens attacking fish with infections or diseases).

Benthic - The bottom of a body of water, such as the seafloor or bottom of a lake where flora and fauna are found.

Bioball(s) - A biological media that is used in filters. Normally are made of plastic, in a spherical shape, and have designs on the outside to attach the growth of beneficial bacteria.

Biological Filtration - The use of filter media to grow colonies of aerobic and anaerobic bacteria to remove ammonia and nitrite from the water.

Bioluminescent - Microbes and animals that can produce their light.

Biomass - Refers to the total mass of living matter within a specified area (normally referred to as bioload).

Biomechanical - The use of filter media that contains both mechanical and biological filtration inside of one unit.

Bleaching - The process in which zooxanthellae expel themselves from corals causing a lack of pigmentation in the given coral.

Blushing - A pink or reddish appearance normally associated with a fish.

BPM - Bubbles Per Minute is a term used to measure the amount of carbon dioxide bubbles that are released into the water when using a CO2 system.

Brackish - Water that has a slight salt content with a specific gravity between 1.006-1.015. Found naturally where rivers meet the ocean.

Bubble Nest - Appearing like small bubbles that look like foam, commonly created when there is a large protein content in the water or created by anabantoid fish when they are searching for a mate.

Buffering - The capability of something to resist changes in pH.


Carnivore - An organism that primarily feeds on a meat-based substance for its diet.

Chemical Filtration - The process of removing particles in the water through chemical reactions (commonly done by using carbon or resins).

Chiller - Equipment that is used to cool down water (opposite of a heater) when it reaches a certain temperature, frequently used with saltwater-related setups but also can be found in freshwater setups dependent on the environment and species that are housed within.

Cycling - The term used for the process of creating The Nitrogen Cycle within an aquarium, which creates nitrifying bacteria.


Doser - A liquid distribution device that is either gravity or mechanically managed to maintain specific water parameters or levels.



Filter - Equipment that is used to remove various levels of impurities from aquarium water through biological, chemical, and/or mechanical methods.

Fry - Recently hatched fish are commonly called fry due to their small appearance.

FOWLR - Fish Only With Live Rock


GH - General Hardness is a measurement of total calcium and magnesium.


Herbivore - An organism that primarily feeds on a vegetable-based substance for its diet.

Hydrometer - A highly sensitive device that measures the specific gravity and salinity of the water. Commonly used in saltwater-related setups.


Internal Filter - A filtering device that is placed within the aquarium, in either a partially or fully submerged state.



KH - Also referred to as dKH, is a measurement of bicarbonates and carbonates and is also known as total alkalinity or acid-neutralizing capacity.


LFS - Local Fish Store (or Shop)

Light Meter - A highly sensitive piece of equipment that measures the intensity of light underwater.


Mechanical Filtration - The process of removing particles in the water through mechanical processes by using various filter media to remove debris, fish waste, uneaten food, and other particle matters.


Nitrate - A toxic byproduct of the nitrogen cycle that is the least toxic nitrogen byproduct often used by live plants.

Nitrite - A toxic byproduct of the nitrogen cycle that is often broken down and used by plants in a planted aquarium or can be removed with water changes.


Omnivore - An organism that feeds on both meat & vegetable-based substance for its diet.


PAR - Photosynthetically Active Radiation is the wavelength of the light spectrum that is created from your aquarium light (or the sun) and is normally measured from under the water to the bottom or wherever you are planning to keep any plant/coral species.

pH - Measurement of relative alkalinity or acidity within a specific type of liquid. A pH reading of 7.0 is considered neutral, higher than 7.0 being a base/alkaline, and readings lower than 7.0 are acidic.

PPM - Abbreviation for Parts Per Million that is used as a measurement of a particular element commonly used in test kits.


Quarantine - The process of dividing newly acquired species or ill species by isolating them in their aquarium for treatment until they are fully cured.


RO - Reserve Osmosis is water that has been fully stripped of all minerals and elements, to only contain pure H2O. It is commonly used to replace evaporated water.


Siphon - Refers to a hose that is commonly used during water changes that use either gravity or suction pressure to transfer water from your aquarium into a bucket or other location.

Specific Gravity - The measurement of relative density or salt content of aquarium water.

Substrate - The material that is placed on the bottom of an aquarium (gravel, sand, pebbles, etc.) that can provide a functional, chemical, and cosmetic purpose.



Undergravel Filter - A filter that is placed underneath a layer of substrate (cannot be sand) that is powered by an air pump or powerhead to suction water into the gravel to use as a biological and mechanical filtration system.



Water Change - The process of removing old aquarium water, and replacing it with a new source of water.

Water Parameters - Refers to specific chemical parameters for maintaining a healthy aquarium, and keeping the aquarium cycle.

Wet/Dry Filters - A filter that exposes beneficial bacteria to both water (wet) and air (dry) for increased biological filtration.