Glossary of Terms

A useful list of commonly used koi pond terms


The ability of living organisms like fish to adapt and adjust to a new climate or

new environmental conditions.



An indication of having a pH (power of Hydrogen) value lower than 7.



Developed in 1912 and used first on WWI soldiers, this compound today is used to fight fungal infections in fish as well as Velvet disease, Columnaris, Lymphocystis and Saprolegnia.


Activated Carbon 

A porous, carbon-based material that effectively eliminates chlorine, contaminants,

pollutants, and other water impurities.


Aeration Pump

An air pump designed to provide ponds with a sufficient amount of oxygen.



Requiring oxygen for an organism to grow and survive.



A gram-negative bacteria found in aquatic environments that can cause infections and

diseases harmful to fishes.



A group of microscopic, eukaryotic organisms that have chlorophyll for photosynthesis.

Single-celled green water algae and multi-celled string algae are its usual forms.



A chemical agent that controls or prevents algae growth.



pH value higher than 7.



Colorless nitrogenous waste product excreted via fish gills that is subsequently poisonous

to fish in even small concentrations. Zero ammonia is the goal in koi ponds.



Requires no oxygen for an organism to grow.


Anal Fin

A fin situated at the ventral median line and behind the anus of a fish.                               


Anchor Worms

Types of copepod crustaceans that are attached to the base of fins and appears like thin,

whitish worm.



A plant that achieves its life cycle within a single growing season.



Oval-shaped, tiny garden pests that are found in clusters of young parts of the plants.


Aquatic Plant

A plant that can adapt and grow in aquatic environments with its roots continually

submerged in water.



Microscopic organisms with only one cell and has no nucleus. There are good bacteria that

help your pond and those that can cause health issues.



This is used to regulate the electrical current to some lighting systems, such as ultraviolet



Ball Valve

A flow control valve that regulates the amount of water passing through the pipe.



A plumbing fitting with ridges that connects vinyl pipes and tubes with equal sizes.



These are two pairs of whiskerlike barbels that are located near the mouth of koi and

functions to locate its food.


Bare Root

A method whereby soil is removed from the roots of the plants that are ready for shipping

and potting process.



This antibiotic is used to treat broad-spectrum bacterial infections (which include Pseudomonas).


Biological Filter

A space in which beneficial bacteria live that function to remove toxins from the water.



One of the main types of wetland ecosystems that accumulates dead plants and is typically

a very low flow environment. 


Bottom Drain

Installed in the pond’s deepest point, it functions as a continuous intake of water and

debris and delivering it to the filtration system.



A solution dissolved in the water for stabilizing pH levels.



A specialized fitting that provides a watertight seal through a plastic container or pond liner.


Caudal Fin

The tail fin of a fish used for forward propulsion.


Check Valve

A valve that allows liquid to flow through a pipe in one direction only thereby keeping dirty

water from going back into the pond.



A chemical that is sometimes present in local water supplies but harmful and poisonous to

fishes. This substance will not evaporate like chlorine will.



A chemical this is commonly used in local water supplies but not healthy for fish as it is

poisonous. It will evaporate in the appropriate time (especially if water is aerated well)



An outdated term referring to living organisms with body temperatures that adapt to the

environmental (ambient) temperature.



Also known as Ichthyobodo necatrix, this flagellate parasite can really cause a lot of health problems for koi.



Interface point of a plant’s stems and roots.  Typically where new shoots arrive from.



A pond treatment that effectively removes chlorine and chloramines from municipal water

for the health and safety of fish.



A natural process that breaks down substances into simpler form performed by bacteria

and fungi.



A unit that floats in the pond to maintain an ice free area of the pond’s surface during winter.


Direct Drive Pump

A pump that has an impeller framework which is connected directly to the motor.


Disappearing Fountain

A water fountain feature in which its water reservoir is not open but hidden in an

underground basin where water can circulate back through the fountain.


State of super decreased activity and metabolism that occurs to koi during winter while living under ice.


Dorsal Fin

A fin located on the backs of marine and freshwater fish species.



A community of living and non-living things that interact as a whole.



A biological catalyst protein that helps speed up a chemical reaction like the breakdown of

organic debris.



Ethylene Propylene Diene Monomer is a synthetic material that is used to make flexible

pond liner.


External Pump

Also known as “in-line pump” it located outside the pond which is equipped with an intake

line going into the pond or skimmer.



A unit designed to effectively clean and clear the pond water.


Filter Media

The material in a filter that either traps debris or provides surface area for beneficial

bacteria in a biological filter.


Fin Rot

A bacterial disease of fish wherein fins become cloudy and white. It is usually followed by

filaments that are separating, fraying, and disintegrating from the tip toward its body. Red

streaks can also be seen throughout the fins.


Fish Lice

A semi-transparent or brownish free swimming circular parasite that can infest fish and

cause spherical, inflamed wounds.


Flex PVC

A flexible version of PVC (PolyVinyl Chloride) that uses the same fittings as standard rigid

schedule 40 PVC pipe.



A treatment that causes suspended organics to clump together then sink to the bottom.


Foot Valve

This valve allows liquid to flow through a pipe in one direction only.



A water feature where the movement of the water and aeration is the ultimate goal.



A Female Pipe Thread or connection type for female internal threads.


Friction Head

Term describing the friction or resistance caused by water flowing through pipes and fittings.



An micro-organism that feeds by absorbing nutrients through its outer cells. Some types

of these organisms will grow on fish and typically appears like cotton.


Gallons Per Hour

GPH is a unit of measure describing the flow of water.


Gate Valve

Also known as a knife valve, this is designed for open or closed operation, but not used for

regulating flow.



General hardness or the measurement of calcium and magnesium ions in water.



Highly vascularized, fleshy structures comparable to lungs which are essential in aquatic




The ability of plants to withstand and survive harsh cold or hot conditions.



The quality of water primarily caused by excess calcium and magnesium concentration.



A plant that can survive winter temperatures, but this varies on temperature extremes.


Head Pressure

The total of static head, friction head, and pressure head; useful to determine the

performance and size needed for pond pumps.



A living organism that exists naturally within a local region.


In-Line Pump

Also known as external pump located outside the pond which is equipped with an intake

line going into the pond or skimmer.



Plant or animal that spreads quickly, such as the weeds or kudzu



Carbonate hardness is the measurement of carbonate and bi-carbonate ions present in




KW is a unit of electrical power equivalent to 1,000 watts or 1.341 horsepower.



KWH is the basic unit of electrical energy equaling one kilowatt of power applied in one



Knife Valve

Also known as gate valve, this is designed for open or closed operation, but not used for

regulating flow.


Koi Pond

A body of water that is deeper than most water gardens and primarily contains koi. It

typically has aquatic plants and greater filtration and water quality.


Lateral Line 

A series of sensory pores opening to the exterior along the side of a fish.


Magnetic Drive Pump 

A pump with an impeller that is not directly connected to an engine but instead the engine

and impeller are each connected to magnets. As the engine spins its magnet, the other

magnet spins and turns the impeller.


Mechanical Filter 

A mechanical unit that removes and traps particles from the water.



A Male Pipe Thread or connection type for male external outside threads.



NO3 is a form of nitrogen or a product of nitrification by beneficial bacteria. This is less toxic than other forms of nitrogen used by plants.



NO2 is a toxic form of nitrogen or a product of nitrification caused by beneficial bacteria. 



Functions as cover and protection of gills of a fish.



(power of Hydrogen) A measurement of the hydrogen ion concentration in water which determine its acidity or alkalinity levels. Above 7 is alkaline and below 7 is acidic.



An organism that lives by feeding off other host organisms.



Any organism that causes a disease or illness.


Pectoral Fin

The front pair fins used to control the delicate movements of fish.


Pelvic or Ventral Fin

Posterior paired fins that are located in the abdomen or toward the rear.



Any plant that lives for more than three years.



Natural filtration using plants as bio-filters.


Pond Liner

A flexible material that forms a waterproof barrier between the earth and the pond.


Pot Bound     

A plant growing in a pot that is too small for proper leaf and stem growth.



A mechanical filter placed before the pump inlet that helps to minimize pump clogging.


Pressure Head

Additional pressure required by some filters, venturis, and other devices.


Pressurized Filter

A completely enclosed filter that acts as a plumbing extension, that can be located at any elevation.



A gram-negative bacteria found in pond water that can cause infections in fish.



A body of water collected and stored at the head of the waterfall or stream.



An in-ground plant stem that gives rise to both roots and shoots.


Root Bound

A plant never removed from its pot whose roots have become tangled. The roots must be carefully loosened when repotted.



Excess water that flows over the ground and reaches the stream or pond as a result of rainfall. Runoff into ponds should be avoided as it carries with it fertilizer and unwanted chemicals.



The amount of salt dissolved in water.



This unit is usually installed outside the pond that skims debris off the pond’s surface and functions as a mechanical pre-filter.



An organic muck that settles at the bottom of the pond and clogs filters. It is made up of debris such as fish waste, rotten plant materials, etc.


Static Head 

The vertical distance that the water travels from the pond’s surface up to a given point.


Submersible Pump

A water pump that operates underwater.


Trace Elements

Small amounts of chemicals or elements.



A device that converts electrical current down in energy.



An underground storage organ (usually starchy) that can be either part of the stem or the root.


Ultraviolet Sterilizer

A device that uses ultraviolet light to eliminate free-floating algae, bacteria, and other organisms.



A geo-textile material placed between the pond liner and the earth to protect it from puncture.



A plumbing fitting with 2 sections of PVC that can be unthreaded and are useful for disconnecting purposes. Can be removed without cutting the pipe.


Up-Flow Filter 

A filter in which the water enters at the bottom then flows up through the filter media before it exits the filter.



A pattern on plants resembling blotched, edged, or striped with yellow, white, or cream color.



A type of valve used for aerating ponds which draws air into the flowing water, and injects bubbles into the pond.



A flow of water with typically less than 45-degree slope.



A vertical drop of water into a pond.


Waterfall Tank

A basin that fills and overflows with water creating a waterfall.


Waterfall Well  

A unit that sits on a waterfall basin to protect the pump and maintain appropriate water volume for circulation.


Water Garden

A feature that focuses mainly on plants but may also contain fish.



Refers to the opening of a pond skimmer.