These are the parameters that the Sutro measures:
pH
The pH is measured with phenol red (the same substance used in liquid test kits), and its acceptable range for testing is between 6.8 - 8.2 (+/- .2 pH).
The Sutro will give recommendations when the pH is less than 7.2 or greater than 7.8 which is the acceptance range. Every recommendation will aim to adjust the pH to 7.5 as a target value.
Free Chlorine
The free chlorine is measured by DPD, and its acceptable range for testing is between 0 - 5ppm.
The variance that the readings can have will depend on the actual fCl level that is in the water.
- If the readings are between 0 and 2.8 the variance will be (+/- 0.2 ppm)
- If the readings are between 2.8 and 5.0 the variance will be (+/- 0.7 ppm)
Free chlorine levels greater than 10ppm, can result in bleaching of the Sutro DPD reagent. This can result in a lower free chlorine reading than the actual level. It is best practice to keep your free chlorine at around 2-4 ppm unless you're performing a shock.
If the free chlorine is measured below 2.0 ppm the Sutro will recommend raising the chlorine in the water. The maximum free chlorine measurement is 5.0 ppm for the Sutro Monitor, any measurement past 5.0 ppm will show as 5+ in the Sutro app, unless bleaching occurs on the cartridge sensor. (when the fCl levels reach 7-10 ppm or higher)
Secondary Sanitizer (Shock)
The Sutro will recommend the secondary sanitizer (shock) when the free chlorine reaches 1 ppm or less. It is best to remove the Sutro from the water for about 24 hours while you're shocking the pool.
We recommend placing the Sutro in a bucket of water while shocking your pool or spa to continue sampling water and to avoid sucking air into the device.
Bromine
Bromine is measured by DPD and its acceptable range for testing is between 0 - 10ppm.
If the readings are between 0 and 6 the variance will be (+/- 0.4 ppm)
If the readings are between 6 and 10 the variance will be (+/- 1.4 ppm)
If bromine falls below 4.0 ppm the Sutro will give a recommendation to raise it.
Total Alkalinity
Total alkalinity is measured through a titration method proprietary to Sutro due to the small amounts titrated.
The acceptable range for TA readings is between 40 and 200 ppm CaCO3 (+/- 20 ppm of the current reading).
The Sutro will recommend increasing the alkalinity if it falls below 50 ppm. The target value for recommendations is 100 ppm. The ideal range for alkalinity is approximately 80-120 ppm, with the goal of maintaining a pH balance while keeping a neutral calcium saturation index.
Temperature
Temperature is measured hourly and the acceptable range is +/- 3 degrees.
Sutro samples the temperature at a greater depth than most floating thermometers. While the temperature is changing and pools are warming up, there can be a bit of a temperature gradient beneath the surface