Overview
This lecture explains Total Dissolved Solids (TDS) in pool and spa water, how to measure TDS, ideal TDS ranges, and how to manage high TDS levels.
Measuring Total Dissolved Solids (TDS)
- TDS can only be measured accurately with an electronic tester that determines water conductivity.
- Devices like the Hawk multi2 meter display TDS in parts per thousand (ppt) or parts per million (ppm).
- Example: 1.53 ppt equals 1,500 ppm TDS reading.
What TDS Represents
- TDS is the sum of all conductive chemicals dissolved in water except pure H2O.
- Includes calcium hardness, alkalinity, cyanuric acid, chlorides, bromides, sulfates, silicates, chemicals, and organic compounds.
- TDS accumulates as water evaporates and is not replaced with fresh water.
Ideal and Problematic TDS Levels
- Ideal TDS range for pools is 1,000 to 2,000 ppm.
- Above 2,500 ppm, water quality problems may occur.
- Symptoms of high TDS: cloudy water, scaling, algae blooms despite high chlorine, salty taste, more bacteria, and plaster wear.
Managing High TDS Levels
- The only solution for high TDS is to partially or fully drain and refill the pool.
- If draining is not possible (e.g., water restrictions), running the pool system longer may help with symptoms but not TDS itself.
TDS in Saltwater Pools and Spas
- Saltwater pools have naturally high TDS due to salt content.
- To estimate non-salt TDS: subtract salinity reading from total TDS reading.
- Example: TDS 5,000 ppm minus salinity 3,500 ppm equals 1,500 ppm non-salt TDS.
- For spas, add 1,500 ppm to fill water TDS to determine maximum acceptable TDS (e.g., fill water at 700 ppm, max spa TDS = 2,200 ppm).
Key Terms & Definitions
- Total Dissolved Solids (TDS) — Total amount of dissolved substances in water, measured in ppm or ppt.
- Conductivity — The ability of water to conduct electricity, used to estimate TDS.
- Parts per Million (ppm) — Measurement unit for small concentrations of dissolved substances.
- Salinity — Concentration of salt in water, important in saltwater pools.
Action Items / Next Steps
- Test pool or spa water regularly for TDS using an electronic meter.
- For spas, measure fill water TDS and follow spa TDS limits as described.
- Drain and refill water if TDS exceeds recommended levels.