Accuracy & Technology
PoolWaterLAB uses reagent-based photometric measurement to provide objective digital readings of pool and spa water parameters. This page explains how the technology works, what accuracy means in practice, and which conditions can influence measurement results.
How photometric measurement works in pool water testing
Photometric testing measures how much light is absorbed by a prepared water sample after a reagent reacts with a specific parameter. The photometer converts light absorption into a numerical value, reducing subjective interpretation compared to visual color matching methods.
What accuracy means in real-world pool water
Accuracy depends on controlled testing conditions. Under recommended procedures, photometric methods typically show predictable and repeatable variation suitable for routine pool and spa water management.
For most parameters, expected variation is expressed as a percentage of the measured value, while pH accuracy is defined in pH units.
Measured ranges and typical accuracy
| Parameter | Measurement Range | Typical Accuracy |
|---|---|---|
| Free Chlorine | 0.00 – 6.00 ppm | ±10% |
| Total Chlorine | 0.00 – 6.00 ppm | ±10% |
| Chloramines | 0.00 – 6.00 ppm | ±10% |
| Chlorine (High Range) | 5 – 200 ppm | ±10% |
| Bromine | 0.00 – 13.0 ppm | ±10% |
| pH | 6.50 – 8.40 | ±0.10 pH |
| Total Alkalinity | 0 – 200 ppm | ±10% |
| Calcium Hardness | 0 – 500 ppm | ±10% |
| Total Hardness | 0 – 500 ppm | ±10% |
| Cyanuric Acid | 0 – 100 ppm | ±10% |
| Phosphate (Low Range) | 0.00 – 4.00 ppm | ±10% |
| Phosphate (High Range) | 0 – 80 ppm | ±10% |
| Iron (Low Range) | 0.00 – 1.00 ppm | ±10% |
| Copper | 0.00 – 5.00 ppm | ±10% |
| Zinc | 0.00 – 1.00 ppm | ±10% |
| Aluminum | 0.00 – 0.30 ppm | ±10% |
| Ammonia | 0.00 – 1.20 ppm | ±10% |
| Nitrite (Low Range) | 0.00 – 1.50 ppm | ±10% |
| Nitrate | 0 – 50 ppm | ±10% |
| Urea | 0.10 – 2.50 ppm | ±10% |
| Active Oxygen | 0.00 – 20.0 ppm | ±10% |
| Hydrogen Peroxide (Low Range) | 0.00 – 2.40 ppm | ±10% |
| Hydrogen Peroxide (High Range) | 0 – 180 ppm | ±10% |
| Chlorine Dioxide | 0.00 – 11.0 ppm | ±10% |
| Ozone | 0.00 – 4.00 ppm | ±10% |
| PHMB | 5 – 60 ppm | ±10% |
| Potassium | 0.70 – 12.0 ppm | ±10% |
| Sulfate | 5 – 100 ppm | ±10% |
Factors that can affect readings
- Cloudy or turbid samples
- Incorrect reaction timing
- Expired or improperly stored reagents
- Water temperature outside recommended range
- Fingerprints, scratches, or air bubbles in the cuvette
Best practices for consistent results
- Rinse the cuvette with pool water before testing
- Keep optical surfaces clean and dry
- Follow the specified reaction time for each parameter
- Store reagents according to recommendations
- Repeat a test if results appear inconsistent
Summary
PoolWaterLAB’s photometric technology delivers repeatable digital measurements when used under recommended conditions. Small variations are normal in field testing and reflect sample handling and chemistry, not subjective color interpretation.