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 a inhabitant to move from one water source to another (such as moving from the pet store's tank to your own aquarium).

Acidic - Relates to the pH scale in where 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 in order to survive.

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

Algae - A simple nonflowering 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 where anything that is 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 or female.

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


Bacteria - Referring to microorganisms that are found, which 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 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 are able to produce their own 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 to on 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 it's 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.


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


Herbivore - An organism that primarily feeds on a vegetable based substance for it's diet.

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


Internal Filter - A filtering device that is placed within the aquarium, in a either 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 under water.


Mechanical Filtration - The process of removing particles in the water through mechanical processes by using various filter medias 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 a meat & vegetable based substance for it's diet.


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 a measurement of a particular element commonly used in test kits.


Quarantine - The process in dividing newly acquired species or ill species by isolating them into their own 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 uses 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 health aquarium, and keeping the aquarium cycled.

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