A liquid or dry compound used to reduce the pH of swimming pool or spa water. See Sodium bisulfate.

Microscopic plant-like organisms that contain chlorophyll. Algae are nourished by sunlight (carrying out photosynthesis). They are introduced by rain and wind and grow in colonies, producing nuisance masses. These organisms include green, blue-green or black, brown, and yellow-green (mustard) algae. Pink/red colored algae-like organisms exist but are bacteria and not algae. There are 21,000 known species of algae.

A natural or synthetic substance used for killing, destroying or controlling algae. (Also spelled Algicide)

The amount of bicarbonate, carbonate or hydroxide compounds present in water solution. See also Total Alkalinity.

An aluminum sulfate compound used to cause suspended solids in the water to congeal into filterable masses (flocculate).

A term used in rating chlorine-containing products as to their total oxidizing power. (also see free available chlorine.)