A device that removes undissolved particles from water by recirculating the water through a porous substance (a filter medium or element).

Usually refers to powder-like substance such as diatomaceous earth or volcanic ash used to coat a septum-type filter. Can also be used as an aid to sand filters.

A device within a filter tank designed to entrap solids and conduct water to a manifold, collection header, pipe or similar conduit and return it to the pool or spa. A filter element usually consists of a septum and septum support, or a cartridge.

A finely graded material (such as sand, diatomaceous earth, polyester fabric, anthracite, etc.) that removes filterable particles from the water.

A chemical substance or compound that promotes the combination, agglomeration, or coagulation of suspended particles in water.

That portion of the total chlorine remaining in chlorinated water that is not combined with ammonia or nitrogen and will react chemically with undesirable or pathogenic organisms.

A dry mixture of cement and sand, Sprayed onto contoured and supported surfaces to build a pool or spa. Water is added to the dry mixture at the nozzle.

The amount of calcium and magnesium dissolved in water; measured by a test kit and expressed as parts per million (ppm) of equivalent calcium carbonate.

Also called Muriatic acid when diluted. A very strong acid used in pools or spas for pH control and for certain specific cleaning needs. A by-product of the addition of chlorine gas to water. Use extreme caution in handling. See also Muriatic acid.

The most powerful disinfecting form of chlorine in water.

A family of chemical compounds, including Calcium hypochlorite, Lithium hypochlorite. Sodium hypochlorite, etc., found in various forms for use as a chlorine carrier in pool and spa water.

The rotating vanes of a centrifugal pump; its action creates the flow of the water.

The water entering a filter or other device.

Families of pool sanitizer products that are self-stabilizing by containing cyanuric acid. Also called Stabilized chlorines.

A solid white granular form of inorganic chlorine that has a pH of approximately 9 and contains available chlorine content (ACC) of 35 percent.