A value expressing the relative acidity for basicity of a substance, such as water, as indicated by the hydrogen ion concentration. pH is expressed as a number on the scale of 0 to 14, 0 being most acidic. 1 to 7 being acidic, 7 being neutral, 7 to 14 being basic and 14 being most basic.

A dye that is used to measure pH.

A type of interior finish (a mixture of white cement and aggregate, which could be tinted or colored) which is applied to a concrete pool or spa. Also called Marcite or Marblite.

An abbreviation for parts per million. The unit of measurement used in chemical testing which indicates the parts by weight in relation to one million parts by weight of water. It is essentially identical to the term milligrams per liter (mg/L).

The coating of filter aid on the septum of a diatomaceous earth type filter at the beginning of each filter cycle.

The difference in pressure between two parts of a hydraulic system, such as the influent and effluent of a filter.

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