09/22/2017 | ORP | 4 MINUTE READ

4 Common Pool Monitoring Mistakes (And How to Avoid Them)

outdoor pool

At Sensorex, we’ve been helping pool owners and operators keep their water safe and clean for a long time. When it comes to pool water monitoring systems, we’ve seen it all. But there are a few pesky mistakes that we see time and again. Avoiding these pitfalls is often easy, and it can save you a lot of hassle.

1. Forgetting to clean and calibrate your sensors

Sensor maintenance may not be glamorous, but it is necessary. Whenever we get a call about a sensor not reading correctly, we always check to see if the user has been cleaning and calibrating their probe regularly. The majority of sensor users don’t actually know that probes need to be cleaned and calibrated to deliver accurate, stable measurements. In fact, many users (even some pool maintenance technicians) will assume that a sensor has reached the end of its life and throw it out.

Ideally, pool sensors should be checked once a month and cleaned or calibrated if needed. Many pool maintenance companies will provide this kind of regular service. If your sensors aren’t getting checked regularly and the readings seem to be off, always try cleaning and calibrating first.

2. Leaving sensors out during the winter

Have an outdoor pool? Live in a place where it snows? Careful not to leave your sensors out during the winter. When temperatures drop below freezing, the liquids and gels inside the sensor body will freeze. If the reference solution is frozen, the sensor will not respond. Freezing can also cause other issues, such as when the volume of the solution expands, dislodging other sensor components.

When sensor reference solution freezes, bubbles form inside the sensor body. If your sensor is transparent, look for these bubbles to identify if it has been frozen. Sensors that have been frozen cannot be repaired; a new sensor should be installed.

If you notice that your sensor is slow to respond, and the temperature is close to freezing, try warming the sensor back up. Usually, a sensor that is cold but not frozen will function properly when returned to the normal temperature range. To avoid freezing your sensors, store them in an insulated place—avoid the garage, if it gets cold in there—when you stop using your pool for the season.

3. Mistaking an ORP measurement for a direct chlorine (ppm) measurement

Measuring oxidation reduction potential (ORP) is a safe and very common way of verifying whether your pool has the correct level of chlorine. However, ORP is not a direct measurement of chlorine. Direct chlorine measurements are given in parts per million (ppm), and many pool owners and operators know that the recommended level of chlorine is 1.0-3.0 ppm. ORP probes measure the sanitization activity of chlorine by measuring its ability to oxidize contaminants in the pool. An ORP measurement is expressed in millivolts, not ppm. The minimum recommended ORP value for a pool is 650mV.

If you are concerned that your probe is returning the wrong readings, test it out by measuring the ORP of a calibration solution. If the probe returns the proper readings, then it is likely functioning correctly. If you require a direct measurement of chlorine in ppm, you can obtain this type of reading using an amperometric free chlorine sensor.

4. Forgetting about cyanuric acid

The use of cyanuric acid has become very popular in the treatment of outdoor swimming pools. Cyanuric acid is a conditioner that forms bonds with free chlorine, which protect the chlorine from dissipating under the sun’s UV rays. This is great news for pool maintenance, as it means that chlorine does not need to be adjusted on a daily basis, as was once the case.

Many powdered chlorine additives today contain cyanuric acid. This becomes tricky, because while chlorine is consumed as it disinfects pool water, cyanuric acid is not. Therefore, if chlorine and cyanuric acid are continually added, the cyanuric acid will build up over time. If the cyanuric acid content of a pool is too high (over 100ppm), then it actually has an adverse effect on chlorine sanitization.

When too much cyanuric acid has built up in a pool, you may observe a drop in oxidation reduction potential (ORP). Many people will assume that the drop in ORP is due to an issue with their ORP sensor. However, if your ORP sensor is reading correctly in a calibration solution, then the culprit may be cyanuric acid build up. Anyone maintaining a pool with chemical additives should be aware of the effects of cyanuric acid on chlorine and ORP.

Ensuring that your pool monitoring system is functioning properly will help keep your pool water safe, clean, and inviting. Avoiding these four mistakes will help you get the most out of your pool monitoring system.

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Posted by Dominic O'Donnell on September 22, 2017

Sensorex is a global leader in the design and manufacture of quality sensors for water quality and process applications. The company offers more than 2000 sensor packages for pH, ORP, conductivity, dissolved oxygen, free chlorine, chlorine dioxide, UV transmittance and other specialty measurements, as well as a full line of sensor accessories and transmitters. Its expert technical support engineers solve analytical sensor challenges with custom designs and off the shelf products.

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