Air Relief Valve: A valve on a filter that allows air to be discharged.
Algae: Microscopic forms of plant life which enter the pool by rain, wind, dust storms or other means. There are numerous varieties – some are free floating, others grow on walls and surfaces. There are green, black and yellow or mustard types among others. Some are more resistant to chemical treatment than others.
Algaecides: Chemicals that prevent and control algae. Others are designed to kill specific types of visible algae growth.
Algistat: A chemical that inhibits the growth of algae.
Available Chlorine: A term used in rating chlorine products as to the strength of the chlorine available per equal units of measurement. It is usually rated as percent. For example, 90% available chlorine means that 1.0 pound of that chlorine compound has 0.9 pounds of pure chlorine strength.
Backwash: The process of thoroughly cleaning the filter medium and/or elements by the reverse flow of water.
Bacteria: The germs that can contaminate your pool. Introduced by swimmers, dust, rain storms and other elements.
Balanced Water: The correct ratio of mineral content and pH that prevents pool water from becoming corrosive or scale forming.
Calcium Hardness: The amount of dissolved calcium in pool water. This should be approximately 200 ppm to 400 ppm, depending on pool finish. Higher hardness levels can cause cloudy water and scale. Lower levels can harm the pool and its equipment.
Cartridge: The element in a filter that can be removed and cleaned.
Chlorinator: A device to apply or to deliver a chlorine disinfectant to water at a controlled rate.
Chlorine: A chemical element that exists as a gas in its elemental form or as part of a chemical compound which is an oxidant and biocidal agent used in disinfecting pool water.
Chlorine Demand: The chlorine needed to kill algae and bacteria in a pool.
Chlorine Residual: The amount of chlorine remaining after the chlorine demand has been met.
Combined Chlorine: The portion of the total chlorine existing in water in chemical combination with ammonia, nitrogen, and/or organic compounds; mostly comprised of chloramines.
Corrosion: The etching, pitting or eating away of a material by chemical action.
Diatomaceous Earth (DE): Ground fossils used as a filter media in DE filters.
Etching: Corrosion of pool's surface by water that is acidic or low in total alkalinity and/or calcium hardness.
Filter: A device that removes undissolved particles from water by recirculating the water through a porous substance.
Free Available Chlorine: The chlorine which has not combined with other things in the water like algae or bacteria. This chlorine is what is still available for sanitizing and can also be considered the chlorine residual.
Hardness: The amount of calcium and magnesium dissolved in water; measured by a test kit and expressed as parts per million (ppm).
Main Drain: The suction fitting located in the lowest portion of an in-ground pool. It's the principal intake for an in-ground pool's circulation system.
Muriatic Acid (Hydrochloric Acid): Use to lower pH and/or total alkalinity in pool water.
Organic Matter: Perspiration, urine, saliva, suntan oil, cosmetics, lotion, dead skin, leaves, and similar debris introduced to water by swimmers and the environment.
pH: A value expressing the relative acidity or basicity of a substance, such as water, as indicated by the hydrogen ion concentration.
PPM: The 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.
Pump: A mechanical device, usually powered by an electric motor, which causes hydraulic flow and pressure for the purpose of filtration, heating and circulation of pool water.
Reagent: Chemical used to test pool water.
Sanitizer: Any substance that kills germs and bacteria, providing a sanitary water environment.
Shock Treatment: The practice of adding significant amounts of an oxidizing chemical (usually liquid chlorine) to water to destroy ammonia and nitrogenous and organic contaminants in water. Usually requires achieving 10-15 ppm of free available chlorine.
Skimmer: A part of the circulation system that removes debris from the surface of the water by drawing surface water through it.
Superchlorination: This term is often misused within the industry. Sometimes this word is used interchangeably with the term "shock". Other times, this term is used to mean elevating the current free chlorine level by an additional 5.0 ppm. Under this definition, the only way "superchlorination" would also "shock" is if the current free available chlorine level is at least 5-7 ppm.
Total Alkalinity: The ability or capacity of water to resist change in pH. A quantitative measurement of the amount of alkaline in water. Measured with a test kit and expressed as ppm.
Total Chlorine: The sum of both the free available and combined chlorine.
Total Dissolved Solids (TDS): A measure of the total amount of dissolved matter in water, such as calcium, magnesium, carbonates, bicarbonates, metallic compounds, etc.
Vacuum: A device used to clean the underwater surface of a pool or spa by creating suction in a hose line.