Just like everything in life, a result may have many causes. In this case, the result is dull pool water that’s lost its sparkle. It’s relatively common, and one cause, that’s often overlooked, is total dissolved solids, or TDS.

Let’s first define this. Your TDS value is the measure of the sum of all the substances dissolved in your pool water. Freshwater swimming pools should have a maximum TDS value of around 1,500 to 2,000 ppm.

Virtually everything that is added to the pool contributes to an increase in the TDS value, including chlorine, shock, algaecides, clarifiers, and pH remediation products. Even bather-introduced contaminants such as shampoo, hair gel, body lotions, and sweat, contribute to TDS value. TDS may also include any outdoor products like lawn care chemicals that have found their way into the pool. And, plus, don’t forget about evaporation, which leaves behind a higher concentration of TDS.

TDS in your pool can reduce chlorine efficacy, dulling pool water clarity, and allowing algae to bloom.

So, what to do about it?

You have several tools at your disposal. The most obvious, and practical, way to reduce high levels of TDS is to drain and fill. However, you can also remove large amounts of TDS via reverse osmosis and micro-filtration using membrane filters. However, these two methods can be costly and time consuming, so start with the first.