A measure of the total amount of dissolved matter in water, e.g. calcium, magnesium, carbonates, bicarbonates, metallic compounds, etc.

The sum of all resistances in a completed operating system.

Also known as Trichloro-s-triazinetrione. Most common in compressed form (tablets or sticks) with 90 percent or more available chlorine, approximately 55.5 percent stabilizer by weight, and with an approximate pH of 2.9.

Also known as Trichloro-s-triazinetrione. A form of organic chlorine, most common in compressed form (tablets or sticks) with 90 percent or more available chlorine, approximately 55.5 percent stabilizer by weight, and with an approximate pH of 2.9. See also Organic chlorine and Sodium dichloro-isocanurate.

Cloudy condition of water due to the presence of extremely fine particulate materials in suspension that interfere with the passage of light.

The period of time (usually in hours) required to circulate a volume of water equal to the pool or spa capacity.

The speed at which a liquid flows between two specified points, expressed in feet per second.

The device included with a through-the-wall and over-the-wall skimmer that controls the amount of surface water (flow) drawn into the skimmer and filtration system. See Skimmer weir.

The procedure of preparing pools and spas for freezing weather. Includes chemical treatment of the standing water, plus physical and chemical protection of the pool or spa and its equipment against freezing.