Please Stop Using Colorimetric Testing

In Blog, Controllers, Maintenance Tips by David Jerkins

Colorimetric testing is color based. A reagent is added to the pool water sample, it’s held up to the light and judged based on how much color is present. Using free available chlorine as an example, typically this is judged by how pinkish red the water is.

Stop using this testing method. Immediately. It’s not accurate at all. It’s better than a guess, it is the level of accuracy I would give it. It can tell you if the chlorine is 1-2 ppm, or 2-4 ppm, or 3-6 ppm. To me, that is worthless when running a commercial swimming pool. Something for residential pool owners who don’t need accuracy.

Chemistry controllers eventually need to be calibrated. Never use colorimetric to calibrate chemistry controllers. It is a precise tool of automation and if you calibrate it based on the color pink, you will end up with an expensive egg timer.

Obviously, there are caveats to this. If there’s no other real option, for example. pH we have used colorimetric for years. It’s also easier to use as the color changes more clearly compared to free chlorine testing. We can still use photometers that examine the color for us and are much more accurate due to this, but it’s still judging on a color.

I beg all of you to throw out the colorimetric test kits and use titration instead. The Taylor 2006C is the industry standard for a reason. With titration testing, you add drops of reagent and count the number of drops and then multiply by a number to get an accurate result.

Do you prefer to use a fancy photometer? That’s great, those are more accurate and fine to use. They also require periodic calibration just like a chemistry controller. How is the photometer going to be calibrated? By titration, not colorimetric. Even if you have a photometer, a titration test kit must still be maintained as a backup and method to calibrate and confirm the photometer is working properly.

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