By Joe Sweazy
Electronic testing devices for pool and spa water analysis are prevalent these days. Some pool professionals are using them and love them, while others have purchased such sophisticated equipment and allow them to collect dust in a box.
How do you know if an electronic testing tool is the right selection? After all, aren’t all the electronic testers faster, easier to use and more accurate and precise?
The answer is yes . . . and no. There is no single electronic tester available today, unfortunately, that measures 25 parameters, costs less than $50 and has no limitations. For now, the industry must focus on what is available and what should be considered when switching to electronic testing. This may include something as simple as a pocket-style TDS meter or as complex as a nine parameter photometer/colorimeter.
Before discussing the various types of instruments available to measure the quality of pool and spa water, some important factors need to be considered in purchasing an electronic testing device.
When evaluating a new electronic testing solution for your water analysis needs, know that the up-front cost is going to be considerably more than a couple of bottles of reagent or a whole new reagent test kit for that matter. Less expensive, single parameter meters start out around $75 (USD). Multi-parameter instruments will set you back around $150 or more, with some instruments costing close to $1,000.
When considering the investment, also anticipate the cost of additional reagents, including calibration standards. It is often helpful to calculate the costs on a per-test basis, which will allow you to make a comparison to other testing methods or a competitive unit.
A single unit, for example, may be capable of measuring five different parameters. Each parameter may only require one reagent. In comparison, a liquid test used to test the same five parameters would likely require more than one reagent per test (some require as many as three). The costs of operating the electronic meter, therefore, may be better than you might expect by just comparing the costs of the reagents.
How easy does the instrument appear to operate? Review the activation and technique required to complete a test and consider how error may be introduced. This is an especially important question if you perform many tests in a day and/or share the testing responsibility with someone who would have difficulty using the instrument regularly.
Also consider the speed with which the testing is completed. Does it take more or less time than your existing method and what does that mean to you?
Many manufacturers will have operating instructions online. They may even have the complete manual available for free download. It can be very helpful to review this documentation prior to purchasing a new unit.
Accuracy and precision are always big factors when looking to upgrade to electronic testing. It is logical that when using electronic tests, more accurate and precise results should be achieved.
That may not always be the case. Fortunately, this should be easy to investigate. Most manufacturers will provide this information in some form.
Determine the expected accuracy (how close to the actual value) and precision (repeatability) by reviewing the sales materials available for any particular unit. If this information is not available, you may want to ask yourself ‘why not’?
Does the unit require periodic calibration and, if so, how difficult is it to perform? Many instruments require some form of calibration.Make sure to understand the recommended frequency of unit calibration. The cost of calibration standards should also be known in advance, in order to avoid the surprise of spending $40 or more on the appropriate calibration standards.
Like accuracy and precision information, the limitations of any instrument should be readily available. Pay careful attention to the operational ranges of the instrument to be sure that it will meet your testing needs.
Take note of any interfering substances that would affect test results. It would be a shame to purchase an instrument that is not recommended for use when hardness levels exceed 500 ppm if the hardness in your area is at least that high straight out of the tap.
Manufacturers may not be as forthcoming with the interference information, but this information is necessary and obtainable nonetheless. For example, pH and temperature limitations for ORP are well documented and plenty of information is available on this topic.
Taking all of the noted factors into consideration, a wise decision can be made about the meter that best fits testing needs. Regardless of the instrument selected, the real benefit is that it can eliminate some of the guesswork that is typically required.
Many users find comparing a reacted color to a color standard very difficult, if not impossible. Instruments may be ideal for those with poor color acuity or some form of color blindness.
However, switching to electronics does not necessarily protect users from themselves. User error can still contribute to inaccuracies, as is the case with any testing method.
For some of the parameters regularly measured in pool and spa water, an analysis can be performed with a simple push of the button. For example, pH can be measured by a portable pH electrode that can be partially submerged into the pool or spa and the appropriate button pushed to activate the reading.
Unfortunately, this technology does not test all the important parameters in pool and spa water. These sensors typically measure pH, TDS, salt, ORP and temperature.
The latest in sensor/electrode technology allows some or all of these parameters to be measured on one unit at a price that is not a major investment. Several manufacturers now offer systems that are capable of measuring pH, TDS, salt, ORP and temperature in seconds, all with the same instrument. The least expensive of these instruments typically sells for around $350.
ORP and pH are measured in much the same way by these types of systems. Voltage is generated between a reference electrode and a measuring electrode with pool water in between.
A change in the current equals a change in the measured value. Even though there are two electrodes, these are often contained inside a single unit, giving it the appearance that it is just one probe. It is important to point out that ORP does not replace regular monitoring of free available chlorine. Regulations require testing free chlorine even in systems fit with ORP-monitoring ability.
Conductivity results are used to approximate total dissolved solids and salt. Conductivity is the measure of the water’s ability to conduct an electrical current.
A reference solution with known concentrations is used as a calibration standard. The unit then assumes the water ‘makeup’ is similar to that of the standard and measures its ability to conduct an electrical current that is converted into a salt or TDS reading, depending on the setting and calibration.
This is really just an approximation as conductivity, however, not a direct measurement of total dissolved solids or salts. But it is a fast and easy method that can provide a close approximation. Advantages include electrode systems that provide near instant results for the parameters that they are capable of measuring. Often the same unit can measure several parameters by switching modes. No additional reagents are needed for regular testing.
The results can also be highly accurate and precise depending on the instrument. These instruments are typically easy to use and operate with little or no training required. This technology is also suitable for continuous on-line monitoring.
The disadvantages are that electrodes require careful handling and cleaning/rinsing after each use with distilled or deionized water. It is also important to carefully follow the manufacturer’s recommendation for storage of the electrodes. These systems also require periodic calibration and it may be difficult to tell when they are not reading accurately.
This type of electronic instrument is often referred to as a photometer or colorimeter. Either way, the basic technology is the measurement of light intensity at defined wavelengths as it passes through a reacted sample. A calculation based on a set calibration curve allows the measured value to be converted to appropriate value of the measured parameter.
This technology continues to improve as reagent technology improves. As great as these systems can be, they are reliant on the reagents (liquid, tablets or powder pillows) for getting accurate measurement. As reagents are improved and use life is extended, therefore, colorimeters become more accurate and reliable.
Additionally, the cost of these systems has dropped some in recent months, as low-cost optics and internal components become available. Some multi-parameter colorimeters can now be had for less than $150.
Most significant pool and spa parameters have the advantage that they can be measured with this technology, with several available in combinations with as many as 25 tests available on one unit. These instruments provide a high degree of accuracy and precision. They will typically meet all regulatory requirements for testing. Most parameters require only a single reagent for testing.
Disadvantages are that reagents are required for this testing. This adds cost and handling concerns. Additionally, these systems may take a longer time to complete tests due to the mixing and testing completion times.
Reflectance testing is the newest technology to enter into the pool and spa market. This type of system utilizes test strips instead of reagents to measure the intended water parameters.
A test strip is reacted and placed on the clear channel where light is reflected off of the reacted test pads. The reflected value is then read by an optical reader that allows for a colorimetric measurement. This measurement is then converted by complex algorithm to calculate concentrations of the measured parameters. Such technology has been used in the past in the medical industry for measuring blood glucose levels.
Advantages are that quick and easy tests for a few critical parameters can be done at one time. For example, a three-way test for free chlorine, pH and alkalinity can be completed in 30 seconds. The cost of replacement reagents is very low, as test strips are generally inexpensive. The up-front cost of these systems is also very inexpensive compared to other electronic testing
The technology is dependent on test-strip results in order to calculate the water analysis, which is a disadvantage. Test strips also will yield slightly more variation and, therefore, less precision than other comparable methods. Plus, not all parameters are currently available.
When selecting an electronic testing instrument there is much to consider. Keep the types of electronic testers in mind as well as their advantages and disadvantages to determine which unit is the best.
About the author
Joe Sweazy is Technical Sales and Services Manager for HACH Company/ETS Business Unit, manufacturer of numerous water quality products and test devices in use around the world. He has published more than a dozen articles on pool and spa water chemistry and has presented numerous seminars at conferences of the Association for Pool and Spa Professionals (APSP) and at the World Aquatic Health™ Conference. He may be reached at email@example.com.