Electronic testing devices for water analysis seem to be everywhere these days. But some service professionals are still hesitant to use them, perhaps because they don’t understand how these systems work.
Taking cost, ease-of use, precision and calibration into consideration, you can make a wise decision about the meter that best fits your testing needs. Regardless of the instrument you choose, the real benefit is that it can eliminate some of the “guesswork” that is typically required.
For some of the parameters regularly measured in pool and spa water, an analysis can be performed with the simple push of a 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 allow for testing of all important parameters. Typically, these sensors will only measure pH, total dissolved solids (TDS), salt, ORP and temperature.
The latest in sensor/electrode technology allows some or all of these parameters to be measured on one unit starting at around $350. Several manufacturers now offer systems that are capable of measuring pH, TDS, salt, ORP and temperature in seconds, all with the same instrument.
ORP and pH are measured by these types of systems in much the same way. 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 TDS 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 “make-up” is similar to that of the standard and measures its ability to conduct an electrical current, which is converted into a salt or TDS reading, depending on the setting and calibration. Unfortunately, this is really just an approximation, as conductivity is not a direct measurement of TDS or salts. However, it is a fast and easy method that can provide a close approximation.
Advantages. Electrode systems provide near instant results for the parameters they are capable of measuring. Often several parameters can be measured by the same unit simply by switching modes. No additional reagents are needed for regular testing. The results also can 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 online monitoring.
Disadvantages. The electrodes require careful handling and cleaning/rinsing after each use with distilled or deionized water. It is 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 gets better. As great as these systems can be, they are reliant on the reagents (liquid, tablets or powder pillows) for getting accurate measurement. Therefore, as reagents are improved and use life is extended, 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 go for less than $150.
Advantages. Most all significant pool and spa parameters can be measured with this technology, and several combine up to 25 tests on one unit. These instruments provide a high degree of accuracy and precision. They typically will meet all regulatory requirements for testing. Most parameters require only a single reagent for testing.
Disadvantages. Reagents are required for this testing. This adds cost and handling concerns. Additionally, these systems may take longer to complete tests due to the mixing and testing completion times.
REFLECTANCE METERS Reflectance testing is the newest technology to enter 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 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. This type of technology has been used in the past in the medical industry for measuring blood glucose levels.
Advantages. A quick and easy test for a few critical parameters at a time. For example, a three-way test for free chlorine, pH and alkalinity can be completed in just 20 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 equipment.
Disadvantages. The technology is dependent on test strip results in order to calculate the water analysis. Test strips will yield slightly more variation, and therefore less precision than other comparable methods. Not all parameters are currently available.
There is much to consider when selecting your next electronic testing instrument. Now you are more knowledgeable about how to select an appropriate tester, as well as some of the advantages and disadvantages of the specific methods. Keep these in mind and you will find the unit that is right for you.