PC: Power compact (lighting).

Peat: Peat is a moss, which can be used to decrease the pH.

Pectoral fins: Paired fins located on each side of the fish behind the gill covers.

Pelagic: Organism living in the water of the ocean above the bottom. Pelagic organisms have the ability to swim around or move in some fashion. "Pelagic" is also used to refer (usually) to eggs or larvae set adrift ocean currents.

Pelvic Fins: Located on the bottom of the fish just under the head.

Peristaltic pump: A dosing pump which works by using rollers to squeeze flexible tubing.

pH: A measure of the "power of Hydrogen", or how acidic or basic the water is. A logarithmic scale from 1 to 14; pH of 7 is neutral. Most freshwater fish prefer a pH between 6.5 and 7.5; marine fish between 8.1 and 8.3.

Pharyngeal Teeth: Grinding teeth located in the throat of the fish.

Phosphate: A by-product of fish metabolism and decaying organic matter or introduced into the aquarium for pH control. Can cause excessive algae growth.

Phosphorous: An important trace element, particularly in marine tanks.

Photoperiod: The number of consecutive hours of light in a day.

Photosynthesis: The process by which organisms, usually plants, use the energy contained in light.

Phytoplankton: Tiny plants and algae in the planktonic layer.

Pinnate: "Feather like" Usually used to describe coral polyps.

Plankton: Microscopic organisms, which form the most primitive rung of the food chain. They serve as food for most small aquatic species. Unable to swim against ocean currents.

Pl*co The use of an asterisk in the name Pleco dates to a superstition where people believed that writing the e in Pleco is what killed theirs.

Polyp: The living animal of a coral.

Power filter: A filter, which hangs on the side or back of a tank with an internal pump to draw water through the filter media.

Powerhead: A small submersible pump. Used to create current or to drive under gravel filters, canisters and protein skimmers.

PPM: "Parts per million".

Predaceous: Predatory. An organism that hunts and eats other animals.

Prefilter: This is a small mechanical filter attached to the input of another filter. Usually a sponge.

Protein skimmer: Also called a foam fractionator, sends many small bubbles through a column of water to separate dissolved organic compounds from the water in a marine tank. The air bubbles generate "foam", which contains organic impurities and which is skimmed off to a collection vessel and discarded.

Protozoan: A single-celled, microscopic organism.

QT: Quarantine.

Quarantine tank: A small tank for the purpose of isolating new, sick or injured fish until they can be safely introduced.

R/O: Reverse osmosis.

Ray: Bones in the fins, usually the dorsal fin.

Reactor: Used to force a controlled reaction. An ozone reactor is the most common example.

Redox: "Reduction-oxidation potential" refers to an electrical charge on a molecule that has transformed in a chemical reaction, an indication of how an aquarium will be able to sustain life. A high value is better than a low value.

Resin: Used for chemical filtration through ion exchange.

Reverse Osmosis: A process for filtering tap water before it is used in an aquarium. This process generates water slowly and wastes a couple of gallons of water for each gallon of filtered water produced. High-pressure water is forced through a membrane, which allows particles of water (and very few other elements) to pass through while the excess is carried off by the wastewater current.

Reverse under gravel filter: An under gravel filter set to run in the opposite direction, pushing water up through the gravel. Sounds good, but in practice not particularly effective.

Rhizome: A stem from which roots and leaves emerge, growing along the surface.

RTBS: Red tailed black shark.

Salinity: The level of dissolved salts.

Salt: A generic term, which scientifically refers to a cation and an anion. However, in aquatics, it refers to the proper combination of inorganic salts, composed mainly of sodium and magnesium chloride.

Scale: A small, flattened, rigid, and circumscribed plate forming part of the external body of a fish.

School: A community of fish of the same species, which swim together as a survival tactic.

Scute: An external bony plate forming protection for catfish.

Sessile: Attached to the substrate.

SG: Specific gravity.

Silicon: A trace element in the marine system. It is an element, which is a building block for many organisms with silica, shells.

Silicon (2): A form of silicon sealant especially made for aquaria. Can also be used to glue rocks or other décor items together for safety. Important to ensure all silicon used is specifically for fish tanks, as many bathroom and kitchen silicons contain pesticides and fungicides to prevent mould and mildew. These are highly toxic to your fish and must never be used.

SL: Standard Length A fish measured from the tip of the nose to the start of the caudal fin.

Soft Water: A water condition with very small amounts of dissolved salts.

Spawning: The production or depositing of eggs by fish.

Species tank: A tank with only one type of fish

Species: Taxonomic designation for the unique name of a living organism.

Specific Gravity: The measurement used in marine systems to determine salinity.

Spectrum: The wavelengths (colour) of light.

Sponge filter: A foam block connects to an airlift tube or, rarely, a powerhead. Water is drawn through the sponge, which acts as both mechanical and biological filter. Excellent for fry tanks, as the tight cells in the sponge and the gentle flow prevent the tiny fish from being sucked into the filter.

Spray bar: A perforated tube which disperses the outflow from a powerhead or canister filter. Can also provide excellent aeration if mounted above the surface of the water slightly.

Strain: A variety of a given species. Some species, particularly livebearers, have huge numbers of strains, usually separated by colour.

Strontium: Trace element necessary for corals, clams, and other marine creatures with calcareous skeletons

Subspecies: A variation in a particular species, usually because of geographical separation.

Substrate: The material used to cover the bottom of the fish tank. Examples include gravel, crushed coral, sand, etc

Sump: A collection container, usually a small aquarium. Used as a holding tank between the tank and the filter.

SW: Saltwater.

Swim Bladder: An internal organ filled with air that helps fish maintain normal buoyancy.

Symbiotic: Two (or more) different organism which are necessary or beneficial to the other's survival

Tannin: Also tannic acid. Soluble group of pale yellow to brown amorphous substances widely distributed in plants, astringent complex phenolic substances of plant origin. Usually introduced into the aquarium by means of bogwood, which leeches tannin for weeks or months, turning the water yellow or brown. Can be removed with activated carbon.

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

TDS: Total dissolved solids.

TL: Total Length. A fish measured from tip of nose to tip of caudal fin

Trace elements: The many necessary elements, usually in very small amounts.

Trickle filter: Biological filtration system, which consists of a chamber with biological filtration media. Water runs through the media, which mixes with the air, promoting bacterial growth.

Tritrate test method: Test in which a reagent is dropped into a sample until a color change is noticed. Tests for hardness are often tritrate tests.

Tubercle: Small white bumps on the gill covers. Usually on cyprinids.

Turbulence: Disturbance of the water.

Turnover rate: The number of times a volume of water equivalent to the volume of the tank is passed through the filter.

TWP: Tap water purification.