TOTAL DISSOLVED SOLIDS The term total dissolved solids (TDS) refers to the concentration of conductive chemicals, bather waste, and other solids that can accumulate in the water, particularly when the water evaporates. You cannot see these solids because they are dissolved in the water, but this does not stop them from corroding metal parts. High TDS also reduces sanitizer efficiency and can make water taste salty. TDS should never be allowed to exceed 1,500 ppm over the start-up level, which is the amount of total dissolved solids measured when the spa is initially filled with fresh water.
TDS is a major concern for spas because of the high water temperatures, which lead to fast evaporation and quick concentration of dissolved solids. Plus, the bather load is heavy in a spa compared to that of a pool, meaning that higher concentrations of solids are introduced to the water via sweat, body oil, soap, shampoo, sunscreen, and even urine.
Testing Total Dissolved Solids. TDS can be
tested only with a liquid test kit designed for professional use. If high TDS is a concern, you should take a water sample to a pool and spa supply store for professional testing.
Adjusting Total Dissolved Solids. The easiest way to lower TDS in a spa is to replace some or all of the water with fresh water. Even if the source water is hard and contains lots of dissolved solids, it will still contain fewer dissolved solids than the used water in your spa.