ACID: a chemical, which lowers the pH when added to the water

ACID DEMAND: amount of acid required to lower pH and total alkalinity of pool water to correct level

ALGAE: microscopic aquatic plant life, which can grow on pool surfaces or float freely in the water. Though harmless, algae discolor the water and indicate improper sanitation.

ALGAECIDE: chemical used to kill or inhibit growth of algae

ALKALINITY: various chemicals and salts in the pool water that increase pH

AVAILABLE CHLORINE: free or combined chlorine used to disinfect pool water


BACKWASHING: cleaning pool filter by reversing water flow

BROMINE: chemical used for disinfecting spas mainly (in same family as chlorine)


CAVITATION: water is boiling in a pump. The flow of water from the suction lines is restricted, which causes a vapor lock at the impeller. Commonly recognized by a rumbling noise in the pump.

CHLORAMINE: chemical compound of nitrogen and hydrogen that combines with free chlorine in pool water. Chloramine causes burning eyes, skin irritation, and chlorine odor.

CHLORINE: chemical used for disinfecting swimming pools

CHLORINE DEMAND: amount of chlorine required to destroy bacteria in pool water

CHLORINE RESIDUAL: amount of chlorine remaining in pool water after chlorine demand has been satisfied

CORROSION: chemical reaction that causes deterioration of metal

CYANURIC ACID: (conditioner/stabilizer) acid used in pool water to prevent chlorine loss


DIATOMACEAOUS EARTH (DE): white powder that is manufactured from microscopic skeletons of diatoms

DISSOLVED SOLIDS: calcium, copper salts, magnesium and other minerals that are suspended in water

DPD: chemical reagent that reacts with active chlorine/bromine and turns the water sample pink


FREE CHLORINE: basic chlorine, not combined with any other chemicals, allowing it to be released immediately for disinfecting. This is usually the kind of chlorine used to superchlorinate.


HARDNESS: measurement of dissolved solids in water


MURIATIC ACID: dilute solution of hydrochloric acid used to lower alkalinity


ORTHOTOLIDINE (OTO): chemical reagent that reacts with total chlorine/bromine, and turns water sample yellow


pH: used to describe acid/alkaline balance in pool water. A pH of 7 is neutral. pH values below 7 are acidic. pH values above 7 are basic. The recommended pH for swimming pool water is 7.2 to 7.8. Never allow pH to drop below 7.0 or go above 8.0. 

PHENAL RED: chemical reagent used to measure pH

PPM: parts per million, the accepted measurement of a quantity of substance in water


REAGENT: liquid or powder chemicals used to test concentrations of specific compounds in water

RESIDUAL: amount of a compound existing in water, usually expressed as PPM


SCALE: mineral deposits formed on pool surfaces, inside piping and on the filter as a result of high calcium hardness and high pH

SODA ASH: sodium carbonate used to adjust the total alkalinity by increasing the pH

SUPERCHLORINATION: heavy dose of chlorine added to pool water to "burn out/shock" nitrogen compounds when bacteria, algae or chloramine build-up cannot be reduced by normal treatment


TOTAL ALKALINITY (TA): measurement of alkaline chemicals in water. TA acts as a pH buffer. Too high of a TA prevents easy adjustment of pH. Low TA causes pH to change and fluctuate widely. Proper pool TA is 100 to 125 ppm. 

TOTAL DISSOLVED SOLIDS: total of dissolved material in the water. High total dissolved solids in pool water (over 1500 ppm) can cause poor sanitizer efficiency, cloudy water and odors.