Bromine is a chemical element used to kill microorganisms and oxidize wastes in pool or spa water.

Calcium hardness

Calcium Hardness is a measure of the calcium salts dissolved in water. These are a main component of scale deposits, which are mineral deposits typically found on pool walls.


Chlorine is a chemical used to kill microorganisms and oxidize wastes in pool/spa water.

Combined chlorine

Combined chlorine means nitrogen-chlorine compounds formed by the reaction of a chlorine disinfectant chemical with ammonia and organic nitrogen compounds. Such compounds include perspiration and urine. Another term for combined chlorine is "chloramines".

Cyanuric acid

Cyanuric acid is a chemical commonly used in outdoor pools to reduce photodecomposition of available chlorine. It is sometimes referred to as "stabilizer".


A ground fault circuit interrupter (GFCI) is a device which monitors the flow of electricity from an electrical outlet and has the ability to shut off electric power if it detects current is travelling through an unintended path which could create an unsafe condition and produce an electrical shock.


ORP is an acronym for "Oxidation Reduction Potential". It is a measure of the tendency for a solution to either gain or lose electrons. High pH water has more "reducing" agents (-ORP) and low pH water has more oxidizing agents (+ORP).


pH is a symbol that expresses the negative log of the concentration of hydrogen ions. pH ranges from 0 to 14. Pure water has a PH of 7.0. If PH is higher than 7.0, the water is said to be basic, or alkaline. If the water’s pH is lower than 7.0, the water is acidic. As pH is raised, more ionization occurs and chlorine disinfectants decrease in effectiveness.

Total alkalinity

Total alkalinity refers to the acid-neutralizing capacity of water which indicates its resistance to changes in pH. Typically, the higher the total alkalinity, the greater the resistance to pH change.