On a service route, total dissolved solids (TDS) is one of the least actionable parameters you can test. It is often included on reports, but in most residential pools it provides little practical value compared to parameters like pH, alkalinity, or chlorine.

Why We Test TDS

TDS measures the total amount of dissolved material in the water — salts, minerals, metals, and byproducts. It increases over time as chemicals are added and water evaporates, leaving solids behind.

In theory, very high TDS can affect water clarity, taste, and corrosion potential. In practice, those effects are almost always better explained by other parameters such as pH, calcium hardness, or specific contaminants.

What We Are Measuring

TDS is not a specific substance — it is the sum of all dissolved ions, including sodium, chloride, calcium, bicarbonate, and others. It does not distinguish between “good” dissolved material (like salt in a salt pool) and problematic buildup.

Because of this, a high TDS reading does not tell you what the problem is — only that dissolved material is present.

Methods Of Testing

• Digital conductivity meters are the standard method. They estimate TDS by measuring electrical conductivity and applying a conversion factor.

• Test strips are available but offer limited usefulness and accuracy.

• Conductivity-based readings are fast and repeatable, but they are indirect measurements and depend on calibration and temperature compensation.

Testing Interferences

• Temperature: Conductivity changes with temperature.

Response: use meters with automatic temperature compensation.

• Calibration: Inaccurate calibration leads to misleading results.

Response: calibrate regularly.

• Salt systems: Salt pools naturally have high TDS due to sodium chloride, which can dominate readings without indicating a problem.

What To Do With The Result

In most cases, no action is required based on TDS alone. There is no practical chemical method to reduce TDS. If TDS becomes extremely high (typically well above 1,500-2,000 ppm above source water), the only effective treatment is partial drain and refill.

Operational Approach

TDS should be viewed as a background indicator, not a control parameter.

Focus on what actually affects water quality: pH, alkalinity, calcium hardness, chlorine, and CYA. If those are in range, TDS is rarely a concern.

Most Common Mistake

Trying to correct TDS directly. TDS is not a problem to fix — it is a measurement that reflects everything else in the water.