Acid: A pH below neutral; also refers to a liquid or dry chemical to lower the pH

Alkaline: A pH above neutral; also a chemical used to raise water pH

Balance: A range where the properties of the water are ideal and will not corrode or form scale

Biguanide: A non-chlorine sanitizer, typically sold as a set (a sanitizer, shock, and clarifier) because it cannot be combined with chlorine, bromine, or mineral sanitizers; more expensive than bromine and chlorine; gives water a smooth feel

Bromine: A halogen sanitizer, effective at higher pH but not stable in sunlight; commonly used in hot tubs

Calcium hardness: The amount of calcium suspended in the water

Catalytic cell: In pool and spa water treatment, this is a box containing electrodes that break apart ions so they can join other ions to form algae- and bacteria-killing chlorine

Chelating agent: A product that binds to metals for their removal

Chlorine: A popular and effective swimming pool chemical; both a sanitizer and oxidizer that kills algae and bacteria and destroys suspended dirt particles in water

Corona discharge: A method of making ozone

Cynauric Acid: A chlorine stabilizer

Flocculant: A product to bind particles together so they can be vacuumed out of the pool

Free available chlorine: The amount of chlorine available to sanitize

Ionizer: A device to produce minerals that help sanitize the water

Oxidize: To remove oils, lotions and other unwanted elements from the water by changing them chemically

Ozonator: A device that produces ozone

Ozone: A short-acting sanitizer and oxidizer made from oxygen

pH: The abbreviation for potential hydrogen, this indicates the acidity or alkalinity of pool or spa water.

ppm: parts per million

Salt chlorine generator: A device that turns ordinary salt into chlorine, a sanitizer

Sanitize: Kill bacteria or inhibit bacteria and algae growth

Sanitizer residual: The amount of active chemical available to sanitize

Sequestering agent: A product to coagulate particles and remove minerals or metals from the water

Shock treatment: The addition of concentrated oxidizer to eliminate unhealthy water conditions; "shocking" chemically changes oils, lotions and other unwanted elements so they can be removed from water

Stabilizer: A product added to chlorine that helps it resist breaking down in sunlight

Total alkalinity: The amount of alkaline elements in the pool

Total dissolved solids (TDS): The amount of inert elements in the water

Ultraviolet: UV light (wavelengths shorter than visible light) used for making ozone