Total Dissolved Solids (or TDS) is the measure of the total of all the soluble substances dissolved in the water. It is usually measured by assessing the electrical conductivity of the pool water.
Distilled or pure water has a TDS value of 0 ppm. Drinking water can have a maximum TDS value of 500 ppm according to EPA water standards.
For regular fresh water swimming pools, the maximum recommended TDS level is 1,500 ppm. Values above this can lead to problems such as cloudy pool water, staining of the pool surfaces, scaling, hard water and a salty taste. TDS values of up to 4,000 ppm and more have been noted in some well-balanced pool water so the individual levels of total alkalinity, hardness, conditioner, pH and metals should be considered along with the general state of the pool and its chemical demand. The TDS value should be used as an indicator of the volume of soluble particles in the pool relative to that of the fill water used.
In swimming pools using salt-chlorine generators, the large volume of salt added radically increase the TDS level, so any measurements are redundant due to the addition of salt.
If the pool water has become saturated with contaminants and the TDS level confirms this, the pool should ideally be drained and refilled with fresh water. There is no method to reduce TDS effectively without replacing some or all of the swimming pool water.
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