Ask the Expert: What is TDS and Why is it Important?

TDS, known as Total Dissolved Solids, play quite a significant role in water chemistry. While pH, total alkalinity and calcium hardness levels usually receive more attention, TDS should not be overlooked. In fact, with the use of chlorine generators in some pools, as well as water restrictions in many parts of the U.S., TDS levels have been steadily climbing throughout the country. With that in mind, it is more important than ever to understand what total dissolved solids are and how they work.

TDS is the total of all dissolved solid matter such as minerals, metals, salts and contaminants including lotions, cosmetics, etc.  It also includes the chemicals you use to keep the water sanitized. Basically, anything you put in the pool or hot tub that dissolves into the water adds to the TDS level.

As water evaporates, these minerals, particles, and chemical residues are left behind.

For swimming pools, after years of this matter being left behind, your TDS will become so concentrated that new chemicals you add to the water will be less and less effective. For hot tubs, a high TDS reading is a good indicator that it’s time to drain and refill the hot tub. The maximum level in both a pool and hot tub is 1500 (parts per million (ppm) of TDS. Take a sample of your water to your dealer if you suspect your TDS levels may be causing any of these issues:

• More difficulty maintaining water balance
• Salty tasting water
• Colored or cloudy water
• Corrosion of metal parts (above 4000 ppm)
• Algae growth despite a good sanitizer level
• Faulty test readings on other elements of water balance
• Eye and skin irritation.

If your dealer confirms that your TDS is over 1500 ppm, the only remedy is to dilute the pool or hot tub with fresh water. For pools, drain a foot or so and refill with fresh water. Then have your water tested again. For hot tubs, fully draining, cleaning and refilling the hot tub with fresh water is your best bet.