The Complete Aquarism Glossary

Decode the jargon. Everything you need to know about fish keeping, from "Ammonia Spikes" to "Zebra Danios".

All Terms
Anatomy Aquarium Problems Equipment & Hardware Filtration & Water Flow Physiology Tank Setup Water Parameters

A

Air Breathing Fish
Anatomy
Air breathing fish are species capable of absorbing oxygen directly from the air in addition to using gills.
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Air Pump
Equipment & Hardware
An air pump supplies air to the aquarium, increasing oxygen exchange and powering devices like sponge filters and air stones.
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Ammonia
Water Parameters
Ammonia is a toxic waste compound produced by fish and decomposing matter, and even small amounts can be lethal.
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Ammonia Spike
Aquarium Problems
An ammonia spike is a sudden rise in toxic ammonia levels in an aquarium, often caused by biological imbalance or excess organic waste.
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B

Bacterial Bloom
Aquarium Problems
A bacterial bloom is a rapid growth of free-floating bacteria that causes cloudy water, usually triggered by excess nutrients or a new aquarium setup.
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Biological Filtration
Filtration & Water Flow
Biological filtration uses beneficial bacteria to convert toxic ammonia and nitrite into safer nitrate, maintaining a healthy aquarium environment.
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C

Canister Filter
Filtration & Water Flow
A canister filter is an external aquarium filter that provides powerful mechanical, biological, and chemical filtration for medium to large tanks.
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Chemical Filtration
Filtration & Water Flow
Chemical filtration removes dissolved impurities, odors, and toxins from aquarium water using media such as activated carbon or resins.
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F

Fish Gills
Anatomy
Fish gills are respiratory organs that extract oxygen from water and remove carbon dioxide from the bloodstream.
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Flow Rate
Filtration & Water Flow
Flow rate is the amount of water a filter or pump moves per hour and determines circulation, oxygenation, and waste removal.
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Freshwater vs Saltwater
Tank Setup
Freshwater and saltwater aquariums differ in salinity, fish species, plants, and maintenance requirements, affecting tank setup and care.
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G

Gasping at Surface
Physiology
Fish gasping at the surface is a distress sign where they breathe at the water’s surface, usually caused by low oxygen, poor water quality, or toxins.
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GH (General Hardness)
Water Parameters
GH measures the amount of dissolved calcium and magnesium in aquarium water, influencing fish health, osmoregulation, and plant growth.
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Gill Filaments
Anatomy
Gill filaments are thin, feathery structures within the gills that allow oxygen exchange between water and blood.
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H

Heater
Equipment & Hardware
An aquarium heater maintains stable water temperature, ensuring tropical fish remain within their safe and healthy thermal range.
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K

KH (Carbonate Hardness)
Water Parameters
KH measures carbonate and bicarbonate levels in water and determines how stable pH remains in an aquarium.
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L

Labyrinth Organ
Anatomy
The labyrinth organ is a specialized respiratory organ that allows certain fish to breathe atmospheric oxygen directly from the air.
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Lateral Line
Anatomy
The lateral line is a sensory system that allows fish to detect vibrations, water movement, and pressure changes around them.
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LED Lighting
Equipment & Hardware
LED lighting provides efficient, adjustable illumination for aquariums, supporting fish visibility, plant growth, and natural day–night cycles.
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M

Mechanical Filtration
Filtration & Water Flow
Mechanical filtration physically removes debris, uneaten food, and waste particles from aquarium water, improving clarity and reducing pollution.
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N

Nitrate
Water Parameters
Nitrate (NO₃⁻) is the final product of the nitrogen cycle; moderate levels are safe, but excessive amounts harm fish and plants.
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Nitrite
Water Parameters
Nitrite (NO₂⁻) is a toxic compound formed from ammonia by bacteria and must be converted to nitrate for a safe aquarium.
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O

Operculum
Anatomy
The operculum is a bony flap that covers and protects a fish’s gills while helping regulate water flow for breathing.
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Osmoregulation
Physiology
Osmoregulation is the process by which fish regulate water and salt balance in their bodies to maintain stable internal conditions.
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P

Partial Water Change (PWC)
Tank Setup
A Partial Water Change (PWC) is the routine removal and replacement of a portion of aquarium water to dilute toxins, stabilize parameters, and maintain fish hea
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