As defined by ASTM F1346, Performance Specification for Safety Covers and labeling Requirements for All Covers for Swimming Pools, Spas and Hot Tubs, a barrier (intended to be completely removed before entry of users), for swimming pools, spas, hot tubs or wading pools, attendant appurtenance and/or anchoring mechanisms which will – when properly labeled, installed, used and maintained in accordance with the manufacturer’s published instructions – reduce the risk of drowning of children under five years of age by inhibiting their access to the contained body of water, and by providing for the removal of any substantially hazardous level of collected surface water. These covers may be power or manual.

The precipitate that forms on surfaces in contact with water when the calcium hardness, pH or total alkalinity levels are too high.

Synonymous with Chelating or Metal-complexation agent, a sequestering agent reacts with potential stain-producing metal ions (i.e., copper, iron, etc.) to reduce staining of pool/spa surfaces and associated colored water.

The practice of adding significant amounts of an oxidizing chemical to water to destroy ammonia or nitrogenous and organic contaminants in water.

A mixture of cement and sand applied onto contoured and supported surfaces to build a pool or spa. Shotcrete is premixed and pumped wet to the construction site.

Part of a skimmer which adjusts automatically to small changes in water level to assure a continuous flow of water to the skimmer.

A white powder used to raise pH of the water.

A white powder used to raise the total alkalinity in water.

A granule used to lower pH and/or the total alkalinity in water.

Also known as Sodium dichloro-s-triazinetrione. An organic chlorine, granular in form, approximately 62 percent chlorine; in the dehydrate form, approximately 56 percent chlorine. It contains 58.7 percent stabilizer by weight and has a pH of 6.0. See also Organic Chlorine.

A clear liquid form of an inorganic chlorine compound obtainable in concentrations of 5 to 16 percent available chlorine.

See Cyanuric acid.

The aperture of fitting through which the water under negative pressure is drawn from the pool or spa.

That piping which is referred to as influent.

The practice of adding a sufficient amount of chlorinating compound to water to destroy chlorine demand compounds and any combined chlorine which may be present. Generally the level of chlorine added is 10 times the level of combined chlorine in the water. (See Breakpoint chlorination.)