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
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
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 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
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
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.