Reference
Pool-operator glossary
The water-chemistry, filtration, and pool-math terms you will meet on the pool-operator exam, defined in plain English. 21 terms.
- Backwashing
- Reversing the flow of water through a sand or diatomaceous-earth filter to flush trapped debris to waste. Backwashing restores the filter's flow rate, and knowing when and how to do it is part of routine circulation-system operation.
- Breakpoint chlorination
- Adding enough chlorine to oxidize and destroy combined chlorine completely, breaking it apart so free chlorine can build back up. Reaching breakpoint is how an operator clears the smell and irritation of chloramine-laden water.
- Calcium hardness
- The amount of dissolved calcium in the water. Too little makes water corrosive and aggressive to plaster and grout; too much causes scaling. Calcium hardness is one of the five readings in the Langelier Saturation Index.
- Combined chlorine
- Chlorine that has already reacted with contaminants such as sweat and urine, forming chloramines. It still shows up in a total-chlorine reading but no longer sanitizes effectively, causes the strong chlorine smell, and is usually cleared by shocking the pool to breakpoint.
- Cyanuric acid (CYA)
- A stabilizer that slows the breakdown of free chlorine by sunlight in outdoor pools. Too little lets ultraviolet light burn off chlorine quickly; too much can suppress chlorine effectiveness, which is why health codes set an upper limit an operator must manage.
- Disinfection byproduct
- A compound formed when sanitizer reacts with organic material such as sweat, oils, and urine. Chloramines are the most common example, and they cause the strong chlorine smell and eye irritation people wrongly blame on too much chlorine.
- Entrapment
- The hazard of a swimmer being held against a drain by suction. Federal law, the Virginia Graeme Baker Pool and Spa Safety Act, requires anti-entrapment drain covers and systems on public pools, and entrapment prevention is a safety topic on the exam.
- Filtration rate
- The flow of water through a filter per unit of filter area, measured in gallons per minute per square foot. Each filter type has a maximum rate; exceeding it pushes water through too fast to clean it effectively.
- Flow rate
- The volume of water moving through the circulation system per unit time, measured in gallons per minute (gpm). Flow rate divides into pool volume to give the turnover time, and sizing it to meet a required turnover is a tested calculation. Learn more: the flow-rate calculation
- Free chlorine
- The portion of chlorine in the water still available to sanitize and oxidize. It is the active sanitizer that kills pathogens, and keeping it in the target range is the core daily job of a pool operator.
- Langelier Saturation Index (LSI)
- A water-balance number that combines pH, temperature, calcium hardness, and total alkalinity to predict whether pool water is corrosive, balanced, or scale-forming. A value near zero is balanced; negative water tends to corrode surfaces and equipment, positive water tends to form scale.
- Oxidation-reduction potential (ORP)
- A measurement, abbreviated ORP, of the water's capacity to oxidize contaminants, reported in millivolts. Many automated systems dose sanitizer to hold a target ORP, because it reflects sanitizer effectiveness more directly than the chlorine concentration alone.
- Parts per million (ppm)
- A unit of concentration, abbreviated ppm, equal to one part of a substance per one million parts of water. Sanitizer levels and chemical doses are expressed in ppm, and converting ppm to ounces or pounds is a tested calculation. Learn more: the ppm dosing calculation
- pH
- A measure of how acidic or basic the water is, on a scale from 0 to 14 with 7 neutral. Pool water is kept slightly basic, commonly near 7.4 to 7.6, because pH drives sanitizer effectiveness, swimmer comfort, and water balance.
- Pool volume
- The total amount of water a pool holds, expressed in gallons. It is calculated from surface area times average depth times 7.48 gallons per cubic foot, and it is the starting number for turnover, flow-rate, and chemical-dosing calculations. Learn more: the volume calculation, worked
- Superchlorination (shocking)
- Raising the chlorine level well above normal, also called shocking, to oxidize contaminants and destroy chloramines. Operators superchlorinate to reach breakpoint and restore clear, sanitary water after heavy use or a contamination event.
- Total alkalinity
- The water's capacity to resist changes in pH, acting as a buffer. It is one of the readings that feeds the Langelier Saturation Index. Low alkalinity lets pH swing wildly, while high alkalinity makes pH hard to adjust. Learn more: how it feeds the saturation index
- Total chlorine
- The sum of free chlorine and combined chlorine in the water. Subtracting free chlorine from total chlorine gives the combined chlorine, the used-up fraction that signals the water needs to be shocked.
- Total dissolved solids (TDS)
- The combined concentration of all dissolved substances in the water, abbreviated TDS. High TDS can dull sanitizer performance and cloud water, and TDS is a factor in the Langelier Saturation Index calculation.
- Turnover rate
- The time it takes to circulate a volume of water equal to the entire pool through the filtration system once. It is the pool volume in gallons divided by the flow rate in gallons per minute, and it is one of the core pool-math calculations on the exam.
- Water balance
- The overall relationship among pH, total alkalinity, calcium hardness, temperature, and total dissolved solids that determines whether water is corrosive, balanced, or scaling. The Langelier Saturation Index expresses water balance as a single number. Learn more: how the saturation index is read