AIR-RELIEF VALVE
A brass or plastic, manually operated valve located at the top of a filter tank for relieving the pressure inside the filter and for removing the air inside the filter (called bleeding the filter). Sometimes called a pressure-relief valve.

ALGAE
Microscopic plant-like organisms that contain chlorophyll. Algae are nourished by carbon dioxide (CO2) and use sunlight to carry out photosynthesis. It is introduced by rain or wind and grows in colonies, producing nuisance masses. Algae are not disease-causing, but can harbor bacteria, and can be slippery. There are 21,000 known species of algae. The most common pool types are black, blue-green, green and mustard (yellow or drawn). Pink or red-colored algae-like organisms exist but are bacteria and not algae. Maintaining proper sanitizer levels, shocking and superchlorination will help prevent the occurrence of algae.

AUTOMATIC POOL CLEANER
A pool maintenance system that will agitate or vacuum debris from the pool interior automatically.

BACKFLOW
The backing up of water through a pipe in the direction opposite to normal flow.

BACKWASH
The process of thoroughly cleaning the filter by reversing the flow of water through it with the dirt and rinse water going to waste.

BROMIDE
A common term for a bromide salt used to supply bromide ions to the water so they may be oxidized or changed into hypobromous acid, the killing form of bromine. Used as a disinfectant.

BROMINE
A common name for a chemical compound containing bromine that is used as a disinfectant to destroy bacteria and algae in swimming pools and spas. Available as a tablet or as sodium bromide, a granular salt.

BTU
Abbreviation for British Thermal Unit. The amount of heat necessary to raise 1 lb. of water 1 degree Fahrenheit.

CENTRIFUGAL PUMP
A pump consisting of an impeller fixed on a rotating shaft and enclosed in a casing or volute and having an inlet and a discharge connection. The rotating impeller creates pressure in the water by the velocity derived from the centrifugal force.

CHECK VALVE
A mechanical device in a pipe that permits the flow of water or air in one direction only.

CHEMICAL FEEDER
Any of several types of devices that dispense chemicals into the pool or spa water at a predetermined rate. Some dispense chlorine or bromine while others dispense pH-adjusting chemicals.

CHLORINE NEUTRALIZER
A chemical used to make chlorine harmless. Used in test kits to counteract the bleaching effect of the chlorine or bromine in order to increase the accuracy of pool water tests. Sold as chlorine and bromine neutralizer, it is used to destroy excessive amounts of chlorine or bromine so the high levels will not affect swimmers.

CHLORINE
A term used to describe any type of chlorine compound used as a disinfectant in swimming pool and spa water or to kill, destroy or control bacteria and algae. In addition, chlorine oxidizes ammonia and nitrogen compounds (swimmer and bather waste).

COPING
The cap or top lip on the pool or spa wall that provides a finished edge around the pool or spa. It can be formed, cast in place or precast, or prefabricated of extruded aluminum or rigid vinyl. It may also be part of the system that secures a vinyl liner to the top of the pool wall.

CORROSION
The etching, pitting or eating away of the pool or spa or equipment. Caused by improper water balance, misuse of acid or acidic products or from soft water.

COVER, HARD-TOP
A cover used on pools, spas and hot tubs that rests on the lip (coping) of the pool or spa deck - not a flotation cover. Used as a barrier to swimmers and bathers, and for maintenance and thermal protection.

COVER, SOLAR
A cover that, when placed on the water's surface of a pool, spa or hot tub, increases the water temperature by absorption and transmission of solar radiation; reduces evaporation and prevents windborne debris from entering the water.

DIFFUSER
A porous plate, tube or other device through which air is forced and divided into minute bubbles for diffusion in the water. A diffuser can also be an overdrain on a sand filter. A difuser is also used on a closed-face impeller on a pump to concentrate water flow to the center of the impeller.

DIVERTER VALVE
A plumbing fitting used to change the direction or redirect the flow of water. Some diverter valves are used on pool/spa combinations to allow the use of the spa and then switch the flow back to the pool. A brand name diverter valve is called an Ortega valve, which is sometimes used to describe a diverter valve.

DRAIN
This term usually refers to a plumbing fitting installed on the suction side of the pump in pools, spas and hot tubs. Sometimes called the main drain, it is located in the deepest part of the pool, spa or hot tub. It is not a drain, such as a drain on a kitchen sink. Main drains do not allow the water to drain to waste but rather connect to the pump for circulation and filtration.

FIBERGLASS
Finespun filaments of glass which are available in a rope or mat form. When used in a process with polyester resins, catalysts and hardeners, can be formed or molded into pools, spas and related shapes.

FILTER
A device that removes undissolved or suspended particles from water by recirculating the water through a porous substance (a filter medium or element). The three types of filters used in pools and spas are sand, cartridge and D.E. (diatomaceous earth).

FILTRATION RATE
The rate at which the water is traveling through the filter, expressed in U.S. gallons per minute (gpm) per square foot of filter area.

FLOW RATE
The quantity of water flowing past a designated point within a specified time, such as the number of gallons flowing past a point in 1 minute - abbreviated as gpm.

GUNITE
A mixture of cement and sand sprayed onto contoured and supported surfaces to build a pool. Gunite is mixed and pumped to the site dry, and water is added at the point of application. Plaster is usually applied over the gunite.

GUTTER
An overflow trough at the edge of the pool through which floating debris, oil and other "lighter-than-water" things flow. Pools with gutters usually do not have skimmers.

HAND SKIMMER
A screen attached to a frame which is then attached to a telepole used to remove large floating debris, such as leaves and bugs, from the water's surface.

HEAT EXCHANGER
A device located inside the heater providing for the transfer of heat from the heat source to the water. This is usually a series of metallic tubes with fins located just above the flames.

HEATER
A fossil-fueled, electric or solar device used to heat the water of a pool, spa or hot tub.

LINER
Also called vinyl liner - The vinyl membrane that acts as the container to hold or contain the water.

MAIN DRAIN
This term usually refers to a plumbing fitting installed on the suction side of the pump in pools, spas and hot tubs. Sometimes called the drain and is located in the deepest part of the pool, spa or hot tub. It is not a drain, such as a drain on a kitchen sink. Main drains do not allow the water to drain to waste but rather connect to the pump for circulation and filtration.

NEUTRALIZER
A chemical used to make chlorine or bromine harmless. Used in test kits to counteract the bleaching effect of the chlorine or bromine in order to increase the accuracy of pool water tests. Sold as chlorine and bromine neutralizer, it is used to destroy excessive amounts of chlorine or bromine so the high levels will not affect swimmers.

OXIDIZER
A non-chlorine shocking compound that removes or destroys built-up contaminants and chloramines in pool water without raising chlorine levels as required when "superchlorinating."

POOLSCAPE
A poolscape is a well-integrated living environment combining a quality pool with the functional and aesthetic considerations of the home and landscape.

PUMP
A mechanical device, usually powered by an electric motor, which causes hydraulic flow and pressure for the purpose of filtration, heating and circulation of pool and spa water. Typically, a centrifugal pump is used for pools, spas and hot tubs.

PUMP CAPACITY
The volume of liquid a pump is capable of moving during a specified period of time. This is usually gallons per minute (gpm).

PUMP CURVE
Also called a pump performance curve - A graph that represents a pump's water flow capacity at any given resistance.

PUMP STRAINER BASKET
Pump Strainer Basket - A device placed on the suction side of the pump, which contains a removable strainer basket designed to trap debris in the water flow without causing much flow restriction. Sometimes called a "hair-and-lint trap."

pH Potential Hydrogen 
Indicates the level of acidity or alkalinity of water on a scale ranging from 0-15. A low pH causes etched plaster, metal corrosion and eye irritation. A high pH causes scale formation, chlorine inefficiency and eye irritation. The ideal range for pH in swimming pools is 7.4 to 7.6.

SHOCK TREAT
The practice of adding significant amounts of an oxidizing chemical - (usually non- chlorine oxidizers, such as sodium persulfate or potassium peroxymonosulfate) - to the water to destroy ammonia and nitrogen compounds or swimmer waste.

SKIMMER
A device installed through the wall of a pool or spa that is connected to the suction line of the pump that draws water and floating debris in the water flow from the surface without causing much flow restriction.

SKIMMER BASKET
A removable, slotted basket or strainer placed in the skimmer on the suction side of the pump, which is designed to trap floating debris in the water flow from the surface without causing much flow restriction.

SOLAR COVER
A cover that, when placed on the water's surface of a pool, spa or hot tub, increases the water temperature by absorption and transmission of solar radiation; reduces evaporation and prevents windborne debris from entering the water.

TEST KIT
An apparatus or device used to monitor specific chemical residuals, levels, constituents or demands in pool or spa water. Kits usually contain reagents, vials, titrants, color comparators and other materials needed to perform tests. The most common pool and spa water tests are: pH, total alkalinity, free available chlorine, water hardness, cyanuric acid, iron and copper.

TEST STRIPS
Small plastic strips with pads attached that have been impregnated with reagents that can be used to test pool water for residuals, levels, constituents or demands. The strips are usually dipped in the water, and the resulting colors of the pads are compared to a standard set of colors to determine concentration.

TURBIDITY
The cloudy condition of the water due to the presence of extremely fine particles in suspension that cannot be trapped by the filter because they are too small. Adding a clarifier, such as an organic polymer or alum, will coagulate the particles and make the filter more efficient.

VACUUM
This term can be used to define any number of devices that use suction to collect dirt from the bottom and sides of a pool or spa. Most common is a vacuum head with wheels that attaches to a telepole and is connected to the suction line, usually via the opening in the skimmer. It must be moved about by a person, and debris is collected in the filter.

VINYL LINER
The vinyl membrane that acts as the container to hold or contain the water.

WATER CLARIFIER
Also called coagulant or flocculant - A chemical compound used to gather (coagulate or agglomerate) or to precipitate suspended particles so they may be removed by vacuuming or filtration. There are two types; inorganic salts of aluminum (alum) and other metals or water-soluble organic polyelectrolytes.

WEIR
Also called skimmer weir - Part of a skimmer that adjust automatically to small changes in water level to assure a continuous flow of water to the skimmer. The small floating "door" on the side of the skimmer that faces the water over which water flows on its way to the skimmer. The weir also prevents debris from floating back into the pool after the pump shuts off.