How To Test Saltwater Pools
What is a Saltwater Swimming Pool?
A saltwater swimming pool uses a chlorine generator for disinfection. Swimming pool chlorine generators (also referred to as saltwater pool chlorinators) create chlorine in the pool water directly, removing the need for users to manually add chlorine-based chemicals to the swimming pool. Free available chlorine is continuously produced at a level which is automatically controlled. This has the benefit of removing the need for storage and transport of chlorine-based chemicals. However, as with any equipment, the chlorine generator must be maintained regularly to prevent fouling.
Most chlorine generators require a salt content of 1500–4500 mg/L as sodium chloride (NaCl) in the swimming pool.
There are two types of saltwater systems: ‘in-line’ and ‘off-line’.
In-line chlorine generators
Sodium chloride (or sometimes magnesium chloride) is added to the pool and used to create saltwater. The water passes through an electrolytic cell installed in the swimming pool’s circulation system, which converts chloride to chlorine by electrolysis. Hydrogen gas, chlorine gas and a solution of sodium hydroxide are also generated.
Off-line chlorine generators
Sodium chloride is added to a bulk storage tank to produce a saltwater brine solution which is fed into an enclosed electrolytic cell. The liquid chlorine that the cell produces is then injected into pool water as needed.
Sodium hydroxide and hydrogen gas are generated and removed from the system, so they aren’t added to the pool water.
Saltwater pool maintenance
An efficient saltwater chlorine generator requires salinity to be maintained at a constant level (as defined by the manufacturer, usually between 1500–4500 mg/L). It is recommended to test salinity in the pool weekly. If the salt concentration is too high, it can cause damage to the cell and other pool hardware. However, if the salt level is too low, this can lead to an unsanitary swimming environment as there won’t be enough chlorine produced.
To find guidance on testing other parameters in pool water, please refer to our Pool Chemistry Guide (link to Pool Chemistry Guide).
Measuring Conductivity, TDS and Salinity
Most chlorine generators have sensors built in that will monitor and display the salinity reading based on the conductivity of the pool water. Portable salinity meters work in the same way.
Conductivity and TDS
The more dissolved solids a body of water contains, the more conductive the water becomes. Therefore, by measuring the conductivity of a body of water, it is possible to estimate the total dissolved solids (TDS) content of that water. The conversion of conductivity into TDS is not the same for all water sources. A set of “standard” TDS factors have been devised based on typical salt compositions because the exact salt composition and concentration of a sample is not normally known.
Typical TDS conversion factors are:
- 67 in normal swimming pools
- 55 in saltwater pools
These standard factors are not a perfect solution but are considered a compromise to allow for quicker measurement.
Salinity
Salinity is related to the amount of sodium chloride in the water. It is also estimated using conductivity; the conversion factor is based upon oceanographic research tables.
Palintest Pocket Sensors
Palintest Pocket Sensors are the ideal solution for accurate testing in a saline pool. The Pocket Sensors have Automatic Temperature Compensation (ATC) guaranteeing the highest accuracy in varying temperatures. The Multiparameter Pocket Sensor performs highly accurate testing for five parameters (pH, conductivity, TDS, salinity and temperature). (link to multiparameter pocket meter product)
What is ATC?
All pH and conductivity measurements must take in to account the temperature of the sample. An instrument with ATC removes complications for the user because it automatically compensates for the varying output caused by temperature differences.