Pool Terms

This glossary is a tool for getting acquainted with a variety of pool-related terms. You will be better able to maintain your pool with a basic understanding of the words below. Either browse around or search for a particular word:


Acid:  A chemical compound which releases hydrogen ions into water, decreasing pH.  Products containing muriatic acid or sodium bisulfate are used to lower pH and total alkalinity in pool water.  Also see pH.

Acidic:  When pool water measures below 7.0 on the pH scale.

Acid Demand:  The amount of acid needed to lower pH to the proper level for pool water.

Algae:  Microscopic plants that grow in or around water.

Algaecide A chemical added to pool water to kill algae infestations and prevent their recurrence.

Alkaline:  When pool water measures above 7.0 on the pH scale.  Also referred to as “basic”.

Alkali Demand:  The amount of alkali needed to raise pH and total alkalinity to the proper levels for pool water.  Also see Base Demand.

Alkalinity:  The amount of carbonates and bicarbonates in pool water.  Also referred to as the ability of the water to resist changes in pH.

Ammonia:  A nitrogen containing compounds that combines with free available chlorine to form chloramines.  A known contributor to chlorine demand.

Backwash:  Reversing the flow of water through the filter to clean the elements and filter medium.

Backwash Cycle:  The time needed to backwash the filter and its components using a reverse flow of water.

Bacteria:  Microscopic organisms that can cause infections, diseases and bather irritation.

Bactericide:  A chemical that will kill bacteria.

Balanced Water:  Pool water that has pH, alkalinity and hardness readings to prevent corrosion and scaling.

Base Demand The amount of alkali needed to raise pH and total alkalinity to the proper levels for pool water.  Also see Alkali Demand.

Basic:  When pool water measures above 7.0 on the pH scale.  Also referred to as “alkaline”.

Bather Load:  The number of people in a pool or spa at a particular time or during a specific period of time.

Breakpoint:  The application of an oxidizer or a combination of oxidizers for the specific purpose of destroying chloramines.

Breakpoint Chlorination:  Achieving breakpoint by using chlorine as the oxidizer.

Bromamines:  Bromine-ammonia compounds that have sanitizing capabilities similar to hypobromous acid.

Bromine:  A chemical used in various forms to sanitize pool and spa water.  Forms hypobromous acid in water.

Buffer:  Used to prevent fluctuations in pH.

Calcium Carbonate:  Can form scale when under certain pool water conditions including high pH, high total alkalinity or high calcium hardness.  If scale is formed, the hard deposits with accumulate on pools surfaces and equipment.

Calcium Hardness:  The amount of dissolved calcium in pool water.

Cartridge:  A porous, replaceable element in some filters.

Chelant:  A chemical compound that ties up iron, copper or calcium to prevent scaling and staining.  Also called chelating agent, sequestrant, or sequestering agent.

Chemical Feeder:  A mechanical device that dispenses chemicals in pool water.

Chloramines:  Chlorine-ammonia compounds that can cause chlorine odour and eye irritation.  This compound is a poor sanitizer for pool water applications.

Chlorinator:  A device that dispenses chlorine into pool water in a controlled, gradual manner.

Chlorine The most widely used sanitizing agent for pool water.  Forms hypochlorous acid in water.

Chlorine Demand:  The amount of chlorine addition required before a free chlorine residual can be maintained.

Chlorine Generator:  On-site device that generates its own supply of chlorine.

Chlorine Residual:  The amount of chlorine left to kill new bacteria entering the pool.  Also, the amount of chlorine left after chlorine demand has been satisfied.

Chlorinated Isocyanurate:  A stabilized compound of chlorine and cyanuric acid added to pool water to prevent natural degradation of chorine by sunlight.  Trichloro-s-triazinetrione and sodium dichloro-s-triazinetrione are used for pool water purposes.

Clarity:  The degree of transparency of water.

Coagulant:  A compound added to pool water to gather suspended particles together for filtration.

Coagulate:  Using a chemical compound to gather suspended particles together in pool water for more effective filtration.

Combined Chlorine:  Chlorine in combination with ammonia or other nitrogen containing compounds.  Also see Chloramines.

Contaminated:  An impure condition indicating the presence of bacteria, algae or other undesirable matter in pool water.

Corrosion:  Etching, pitting and other destructive erosion of pool surfaces and equipment due to low pH or other chemical imbalance.

Cyanuric Acid:  A chemical added to pool water to reduce degradation of chlorine by sunlight.  Also called stabilizer.

Diatomaceous Earth (DE) Filter:  A filter that uses diatomaceous earth or volcanic ash as a medium.

Dry Acid:  Sodium bisulfate, added to pool or spa water to lower pH and total alkalinity.

Effluent:  Water flowing out of filter or other device.

Fibreglass:  A pool shell material make of spun filaments of glass.  When combined with resins it can be moulded into any shape and hardened to provide a slick, durable surface.

Filter:  A device that removes waste particles as the water circulates through a porous surface called a filter medium.

Filter Aid:  Usually coats the surface of the filter medium.  Designed to aid in removing smaller particles than the filter medium would normally trap.

Filter Cycle:  The operating time between backwash cycles.

Filter Medium:  A porous component (sand, diatomaceous earth, synthetic fabric, etc.) that removes particles and other suspended wastes from water before it is recirculated back to the pool.

Flocculent (Floc):  A compound that causes small particles of suspended matter to clump together into larger masses.

Flow Rate:  The volume of liquid flowing past a given point in a specific time period.  Expressed in litres per minute (lpm).

Free Available Chlorine:  Hypochlorous acid, the chlorine in pool water that is not combined with ammonia or other nitrogen containing contaminants and is therefore available to kill bacteria or algae entering the pool.

Gunite (Shotcrete):  A concrete and sand mixture sprayed onto a reinforced steel form to create a pool shell.

Hydrochloric Acid (HCl):  A strong acid used to control pH in pools and to acid wash the interior of pools.  Also called muriatic acid.  NOTE:  Use with extreme caution, employing proper safety equipment.

Hypobromous Acid (HOBr):  The active sanitizing form of bromine.

Inlet:  A fitting or port through which water passes into the pool.

Jet:  An inlet fitting through which water returns to the spa or pool at a high velocity.

Laterals:  The horizontal filter grids at the bottom of a sand filter.

Leaching:  The process of extracting a mineral from plaster pool interior (or other pool surfaces).

Nitrogen (N):  An element that can combine with chlorine to form chloramines (combined chlorine).

Outlet:  A pipe from the main drain and/or skimmer(s) used to direct water from the pool to the pump and filter.

Organic Matter:  Pool contaminants typically derived from living organisms.  Include leaves, suntan lotions, cosmetics, urine, perspiration and other swimmer waste and environmental debris.

Organisms:  Algae, bacteria or other living matter that grow in pool or spa water.

Oxidation:  A chemical process for removing irritating compounds from pool water.  It also refers to the rusting or corrosion process that can occur as metal weathers.

Oxidizers:  Agents that help eliminate waste from pool water.  Also, can contribute to the combustion of other material.

pH:  A measurement that indicates the acidity or alkalinity of pool water.  On a scale of 0 to 14, 7.0 is neutral.  Values below 7.0 are acidic, while values above 7.0 are alkaline (basic).

Plaster:  A mixture of white cement and white marble dust applied as an interior finish on concrete and gunite pools.

ppm:  Parts per million, a unit of measurement used in chemical application.  It indicates the amount by weight of a chemical in relation to one millions parts of pool or spa water.  Equivalent to one milligram per litre (mg/L).

Precipitate:  Solid particles forced out of solution.  They may settle to the bottom of the pool or remain suspended in the water.

psi:  Pounds per square inch, a measure of pressure.

Pump:  A motor-powered mechanical device that creates pressure and water flow to allow filtration, heating and water circulation.

Pump Strainer:  The lint and hair trap on the suction side of the pump to remove debris with a minimum of water flow restriction.

Reagents:  Chemical test solutions that can be used to check water for chlorine, pH, total alkalinity or other factors.

Recirculation System:  The pipes, fittings, filters and pumps through which water is circulated in and out of the pool.

Residual:  The amount of measurable compound (such as free available chlorine) remaining in pool water.

Sanitizing The process of killing or inhibiting the growth of bacteria so as to prevent the transmission of disease.

Saturation Index:  A numerical value used to indicate whether the pool water is balanced, scale forming or corrosive.

Scale:  Hard deposits (calcium carbonate) that form on pool surfaces and equipment due to excessive calcium or other out of balance water conditions.

Sequestering Agent:  See chelant.

Shock treatment:  The process of adding an oxidizing compound to the pool water to chemically break up (oxidize) contaminants.

Skimmer:  A device in the pool wall that continuously directs debris and surface water to the filter.  A hand skimmer can be used manually to collect leaves and other large floating debris from the water’s surface.

Stabilizer:  See Cyanuric Acid.

Superchlorination:  Adding enough chlorinating compound to reach a 10ppm free chlorine residual.

Total Alkalinity:  The ability of water to resist changes in pH.  Measured as carbonate present in the water.

Total Dissolved Solids (TDS):  The total amount of dissolved material in water.

Turbidity:  The degree of cloudiness of water.

Turnover Rate:  The time it takes for the circulation system to pass the entire volume of water through the filtration system.  Usually expressed in hours.

Winterizing:  The procedure for protecting pool, spas or hot tubs from freezing condition