Recommended swimming pool and spa pool testing frequency
     High risk pools include spa pools, hydrotherapy pools, baby and infant learn to swim pools, infant wading pools, water features in pools, pools used by incontinent people, or a pool with three or more of the following risk factors:

     pH greater than 7.6 in a chlorinated pool
     consistently poor disinfection (previous chemical
or bacteriological criteria failures).
     high turbidity
     poor pool circulation and/ or filtration
     high bather loads
     presence of algae
     regular use by birds e.g., ducks
     easy access of foreign material e.g., litter
     biofilms detected
     poor quality make-up water (high in chloramines)

FREQUENTLY PARAMETER FOR TESTING:
Chlorine (Free, Combined, Total)
     Chlorine is the common disinfectant for swimming pools. Free chlorine is the form of chlorine available to sanitize and oxidize the water. Combined chlorine is the result of used up free chlorine when it reacts with contaminants. Total chlorine is the sum of the free chlorine and combined chlorine.
Cyanuric Acid (CYA)
     Chemical used mostly in outdoor pools as a stabilizer for free chlorine. It prevents the degradation of chlorine by ultraviolet light. Ppm Abbreviation for parts per million, a common measure of the concentration of a substance in solution. Assume 1ppm = 1mg/ L. pH pH is a measure of the acidity or basicity of a solution.
pH
     ranges from 0-14 with a pH~7 as neutral. pH greater than 7 is characterized as basic (alkaline) and pH less than 7 is acidic.

ORP
   ORP or oxidation-reduction potential is a measure of the tendency of a solution to gain or lose electrons when encountering another chemical. A properly treated and balanced pool should have an ORP of atleast 700 millivolts.

Alkalinity
     Alkalinity is a measure of the buffering ability of water to changes in pH. Higher alkalinity means the water is more resistant to changes in pH.
Hardness
     A parameter of water that measures the quantity of scaleforming ions in solution. Total hardness is the sum of calcium and magnesium ions whereas calcium hardness refers only to calcium ions.
Total Dissolved Solids (TDS)
     A measure of all solids dissolved in water. TDS includes salt in the case of salt-water pools.
OTO (or OT)
     Abbreviation for the chemical reagent orthotolidine originally used for determining chlorine levels. OTO can only measure the total chlorine level and turns the pool water yellow upon addition.
DPD
     Abbreviation for the chemical reagent N, N-diethyl-pphenylenediamine that is used in drop tests to determine both total and free chlorine levels. The pool water sample turns pink upon addition of DPD.
     DPD-FAS This term refers to a variation of a DPD test that uses titration to determine the measure of free and combined chlorine down to 0.2ppm. FAS, ferrous ammonium sulfate, is the reagent added by titration until the solution changes from pink to colorless signaling the endpoint of the reaction.