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Water Testing

Water Testing, Typical Tests performed on Pools.

Understanding water chemistry is the first step to having a pool that is easy to maintain. Never add any chemical without reading the label on the product and testing the water


pH is a measure of the amount of hydrogen ions, that are in solution. The pH scale goes from 0 to 14. Zero is very acidic and 14 is very basic. A reading of 7.0 is neutral. pH affects the swimming pool water, far more than any other parameter. It affects the efficiency of the sanitizer, as well as the overall balance of the pool. pH is measured using a chemical known as phenol red, and the color produced by adding the phenol red to a sample of the swimming pool water. The color produced is compared to colors from known concentrations of hydrogen ions. Alternatively, pH can be tested using test strips. The test strip is dipped into the pool water and compared once again to known standards. Electronic meters are also available for measuring the pH, the pH is read directly from the meter, without comparison to a known color. Acid demand is the amount of acid needed to be added to a pool to lower the pH to the desired range. Base demand is the amount of basic material required to raise the pH to the desired level. To lower the PH, usually dry acid is used, sodium hydrogen sulfate (pH decreaser), to raise the pH, usually sodium carbonate(pH increaser) is used. If the pH is only slightly low, Sodium hydrogen carbonate can be used (Alkalinity increaser). Acceptable pH values are between 7.2-7.8


Total alkalinity is actually the measure of hydroxide and carbonate ions that are present in the water, expressed in units of parts per million (ppm). Alkalinity affects the pools water balance, as well as the acid or base demand. Alkalinity acts as a buffer to prevent the pools pH from bouncing up and down. Acceptable values for alkalinity are between 80-120 ppm. Alkalinity is usually determined by titration. Titration is performed on the water sample, by adding a dye to the water, that changes, when a second chemical (an acid) is added drop wise, until a color change is noted. Alternatively test strips are available to dip and read. As a general rule 25 ounces or muriatic acid or two pounds of PH reducer (powder), will lower the Alkalinity 10 ppm, in a 10,000 gallon pool. Remember to allow, sufficiency time for the chemicals to mix, before retesting, typically 1 cycle of the pump is sufficient. To raise alkalinity, pH increaser, sodium carbonate(also increases pH) or alkalinity increaser, sodium hydrogen carbonate can be used. Until experience is gained it is suggested to use the alkalinity increaser.


Is the amount of calcium and magnesium that is present in the water. Water below 60 ppm is soft water and water greater than 120 is said to be hard. Water does not like to be soft. Water that is soft will attempt to become hard, by dissolving minerals from the environment, typically the pool wall. Water hardness is tested in a manner similar to that already described for alkalinity. Alternatively test strips can be used. Water hardness should be in the range of 150 to 250 ppm. It is increased by adding calcium increaser (calcium chloride) to the water, reducing calcium hardness can be accomplished by dilution with water, with less hardness than is currently in the pool. It can also, be reduced chemically, using Trisodium Phosphate, but this should be left for a pool professional. Calcium levels can increase by prolonged use of calcium based chlorine products. Read the label, if it says calcium hypochlorite ad you calcium levels are high, switch to another form of chlorine

Total Dissolved Solids

Total dissolved solids or TDS is a measurement of all the materials that are dissolved in the pools water. Higher levels of TDS (above 2000), can cause strange phenomena to occur, for example algae growth, where an obviously high present of chlorine is Available TDS is measure using a conductivity meter. Lowering of the TDS is accomplished by replacing the existing water with water that is low in TDS. if TDS is high avoid the use of chemicals that are increase the TDS. An example of this is Liquid Chlorine.

Copper Testing

Copper is introduced into pool water from copper based algaecides or from water that is extremely corrosive and dissolves components that are part of the pool, such as brass valves, impellers or heater components. Copper can cause staining of the pool surface, usually a turquoise stain, swimmers can come out of the pool with green hair or blue fingernails. The standard test for copper is colorimetric, chemicals are added to a sample of pool water, if copper is present a color is produced and compared to known standards. Copper can be removed from pool using chemicals called sequestering agents.

Iron Testing

Low levels or Iron (0.1 ppm) can give water a bitter medicinal taste, higher levels can cause staining, which is often black or rust colored. Iron can be introduced into the pool from the fill water and if the water is corrosive, from the piping and other equipment present in the pool. The standard test for Iron is colorimetric, chemicals are added to a sample of pool water, if Iron is present a color is produced and compared to known standards.

Cyanuric Acid

Cyanuric acid is the conditioner that is added to the pool, to prevent the suns rays from breaking down the chlorine faster that if the conditioner was not present. Typical levels of Cyanuric acid are 40 ppm, it can increase by the use of stabilized products such as Dichlor or Tri-Chlor sanitizer.

Links to Other Water Chemistry Topics

Calcium Deposits

Chlorine Products

Glossary of Chemical Terms

Potassium Monopersulfate

Saturation Index

Spa Disinfectants

Water Testing