Automated water chemistry controllers are becoming a staple for most commercial pools and some residential applications as well. The key to reliable readings is the proper installation and maintenance of the sensors.

Here are some tips on how to keep the controllers on your route working to perfection.

Mounting the sensor

A standard automated chemical controller uses an oxidation reduction potential sensor for monitoring and controlling sanitizers. It also utilizes a sensor for pH control.

Sensors can be mounted directly on the main circulation line. However, it is recommended that this installation method be used only for pipes 2 inches in diameter or smaller. Reason: The tip of the sensor must always be submerged in water. If the sensor is subjected to air or splashing water, the readings could be compromised.

If you have pipe that is larger than 2 inches in diameter, a 1/2-inch bypass line is recommended to mount the sensor. The key to a bypass line is to make sure there is constant water flow. This is done by using the system's pressure differential. The intake side of the bypass line should be installed on the pressure side of the circulation system after the filter. The return side should be installed to a low pressure area such as the vacuum side before the circulation pump.

It is important to protect the sensors as best you can. Running the bypass line after the filter and returning it to the influent side will ensure proper flow and cut down on the possibility that debris will harm the sensor.

Sensor maintenance

With the number of chemical controllers in the field growing, it's more and more likely you'll find an existing unit on your route. Keeping them well-maintained is crucial to getting quality readings.

The sensor tips must be kept clean and free of chemical deposits and contamination. They may need to be cleaned on a weekly or monthly basis, depending on the water quality and other facility-specific characteristics.

A slow response and inconsistent readings usually indicate that sensors are in need of cleaning. Clean the glass bulb at the end of the sensor after removing it from the pipe. Use soap, water and a soft toothbrush or cotton swab. After this initial cleaning, dip the sensor into a little muriatic acid to clean off any remaining oily film.

Next, test the sensors to make sure they have proper pH and ORP readings.

* pH sensor

The pH is the simpler of the two to test because a probe's readings can be matched up with a test kit. Test kits are not an exact science, but if you have faith in the reading and the controller appears slightly off, simply recalibrate to the new number. Recalibration is usually done using the controller keypad.

If the controller is giving a pH reading far higher than the test kit, it could be time to change the probe. In addition, if you recalibrate the sensor down and it drills up soon after, it's time to get a new probe.

Another good test for the pH probe uses muriatic acid. Gently take it out of the fitting tee or flow cell, and hold it a couple of inches over the acid tank. You should immediately notice the pH reading spiraling downward. If the reaction is slow or nonexistent, it's another sign to buy a new sensor.

* ORP sensors

These sensors read oxidation reduction potential, a measurement of sanitizer activity conveyed in millivolts. No calibration is needed. Note: This reading is not to be mistaken for a free chlorine residual count.

ORP sensors are the opposite of pH probes, tending to read low when they reach the end of their life span. If the ORP sensor reads low--yet you have a strong free chlorine residual in the water and the other water chemistry numbers are in the proper range (pH around 7.5, total dissolved solids between 1,000-2,000 ppm, cyanuric acid between 30-50 ppm, according to NSPI)--the sensor may need replacing.

You can test the ORP sensor with an acid tank just as you did with the pH probe. Hold the sensor over the acid tank and you should witness the ORP reading scroll upward immediately. Slow reaction rates and low readings are two signs of an old and tired ORP sensor.

Another good ORP sensor test involves using tap water, which contains a small residual of chlorine. Place the ORP probe in the glass of tap water and you should see the ORP reading react to the new body of water.

You want to see a quick reaction and have the reading stabilize. If the ORP sensor reacts well to the tap water test, place it back in the circulation line and start to test the other water chemistry parameters. High TDS or cyanuric acid levels can force ORP readings to be low.

To determine what a good ORP set point is for your application, feed sanitizer into the pool until the desired ppm residual is reached. Look at the ORP reading on the controller and make it your set point. It's that easy.

McCollum is the assistant sales manager at Chemtrol, based in Santa Barbara, Calif.

COPYRIGHT 2004 Hanley-Wood, Inc.
COPYRIGHT 2004 Gale Group