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everyone who is responsible for operating and maintaining a swimming pool or spa
has to test, monitor, and control complex, interdependent chemical factors that
affect the quality of water bathers are immersed in. Additionally, aquatic
facilities operators must be familiar with all laws, regulations, and guidelines
governing what these parameters should be.
Why? Because the
worst breeding ground for any kind of microorganism is a warm (enough) stagnant
pool of water. People plus stagnant water equals morbid illness. That’s why
pools have to be circulated, filtered, and sanitized – with any number of
chemicals or methods, but most frequently with chlorine compounds. However,
adding chemicals that kill the bad microorganisms can also make the water
uncomfortable, and in some cases unsafe, for swimmers. Additionally, if all the
chemical factors of the water are not controlled, the very structures and
equipment that hold the water and keep it clean are ruined.
So the pool
professional must perform a delicate balancing act with all the factors that
affect both the health and comfort of bathers and the equipment and structures
that support this. Both water balance – or mineral saturation control – and
sanitizer levels must constantly be maintained. This is achieved by measuring
pertinent water quality factors and adding chemicals or water to keep the
factors within acceptable parameters.
constantly changing. Anything and everything directly and indirectly affects the
relationship of its chemical parameters to each other: sunlight, wind, rain,
oil, dirt, cosmetics, other bodily wastes, and any chemicals you add to it.
Balanced water not only keeps swimmers comfortable, but also protects the pool
shell, plumbing, and all other related equipment from damage by etching or
build-up and stains.
professional is already well acquainted with pH, Total Alkalinity (TA), and
Calcium Hardness (CH); along with Total Dissolved Solids (TDS) and Temperature,
these are the factors that influence water balance. Water that is in balance is
neither aggressive nor oversaturated.
lacks sufficient calcium to saturate the water, so it is hungry for more. It
will eat anything it comes into contact with to fill its need, including the
walls of your pool or spa or the equipment it touches. Over-saturated water
cannot hold any more minerals, so dissolved minerals come out of solution and
form scale on pool and equipment surfaces.
The pH of pool
water is critical to the effectiveness of the sanitizer as well as the water
balance. pH is determined by the concentration of Hydrogen ions in a specific
volume of water. It is measured on a scale of 0-14, 0-7 being acidic and 7-14
You must maintain
the pH of the water at a level that assures the sanitizer works effectively and
at the same time protects the pool shell and equipment from corrosion or scaling
and the bathers from discomfort or irritation. If the pH is too high, the water
is out of balance, and the sanitizer’s ability to work decreases. More and more
sanitizer is then needed to maintain the proper level to kill off germs.
Additionally, pH profoundly affects what and how much chemical must be added to
control the balance. A pH of between *7.2 - 7.6 is desirable in most cases.
*As one of the
most important pool water balance and sanitation factors, pH should be checked
hourly in most commercial pools. Even if you have an automatic chemical
monitor/controller on your system, you need to double check its readings with an
independent pH test. With saltwater pools, pH level goes up fast, so you need to
check it more often. Tests are available that require reagents and subjective
evaluation of color depth and hue to judge their pH. But different users
interpret these tests differently, and results can vary wildly.
and ULTRAPEN™ PT2 give instant lab-accurate, precise, easy-to-use, objective pH measurements,
invaluable in correctly determining what and how much chemical to add to
maintain water balance and effective sanitizer residuals.
Alkalinity (TA) is the sum of all the alkaline minerals in the water, primarily
in bicarbonate form in swimming pools, but also as sodium, calcium, magnesium,
and potassium carbonates and hydroxides, and affects pH directly through
buffering. The greater the Total Alkalinity, the more stable the pH. *In
general, TA should be maintained at 80 – 120 parts per million (ppm) for
concrete pools to keep the pH stable. Maintaining a low TA not only causes pH
bounce, but also corrosion and staining of pool walls and eye irritation.
Maintaining a high TA causes overstabilization of the water, creating high acid
demands, formation of bicarbonate scale, and may result in the formation of
white carbonate particles (suspended solids), which clouds the water. Reducing
TA requires huge amounts of effort. So the best solution to TA problems is
prevention through close monitoring and controlling. The POOLPRO™ PS9 Titration Kit features an in-cell conductometric titration for determining alkalinity.
Calcium Hardness (CH) is the other water balance parameter pool professionals are most familiar with. CH represents the calcium content of the water and is measured in parts per million. Low CH combined with a low pH and low TA significantly increases corrosivity of water. As the water becomes more aggressive, the solubility of calcium carbonate also increases. This means that plaster and marcite pool finishes will deteriorate quickly because calcium carbonate is a major component of both plaster and marcite. Low CH also leads to corrosion of metal components in the pool plant, particularly in heat exchangers. Calcium carbonate usually provides a protective film on the surface of copper heat exchangers and heat sinks. This thin layer prevents much water-to-metal interaction but does not adversely affect the heating process. Without this protective layer caused by low CH, heat exchangers and associated parts can be destroyed prematurely. Strangely enough, as water temperature increases, solubility of calcium carbonate decreases. The recommended range for most pools is 200 - 400 ppm. Calcium hardness should be tested at least monthly. The POOLPRO™ PS9 Titration Kit features an in-cell conductometric titration for determining hardness.
Solids (TDS) is the sum of all solids dissolved in water. If all the water
in a swimming pool was allowed to evaporate, TDS would be what was left on the
bottom of the pool – like the white deposits left in a boiling pot after all the
water has evaporated. Some of this dissolved material includes hardness,
alkalinity, cyanuric acid, chlorides, bromides, and algaecides. TDS also
includes bather wastes, such as perspiration, urine, and others.
TDS is often
confused with Total Suspended Solids (TSS). But TDS has no bearing on the
turbidity, or cloudiness, of the water, as all the solids are truly in solution.
It is TSS, or undissolved, suspended solids, present in or that precipitate out
of the water that make the water cloudy.
High TDS levels do
affect chlorine efficiency, algae growth, and aggressive water, but only
minimally. TDS levels have the greatest bearing on bather comfort and water
taste – a critical concern for commercial pool operators. At levels of over
5,000ppm, people can taste it. At over 10,000ppm bather towels are scratchy and
mineral salts accumulate around the pool and equipment. Still some seawater
pools comfortably operate with TDS levels of 32,000ppm or more.
As methods of
sanitization have changed, high TDS levels have become more and more of a
problem. *The best course of action is to monitor and control TDS by measuring
levels and periodically draining and replacing some of your mature water with
new, lower TDS tap water. This is a better option than waiting until you must
drain and refill your pool, which is not allowed in some areas where water
conservation is required by law. However, you can also decrease TDS with
desalinization equipment as long as you compensate with Calcium Hardness. (Do
not adjust water balance by moving pH beyond 7.8.)
Regardless, you do
need to measure and compensate for TDS to get the most precise saturation index
and adjust your pH and Calcium Hardness levels accordingly. *It is generally
recommended that you adjust for TDS levels by subtracting one tenth of a
saturation index unit (.1) for every 1,000ppm TDS over 1,000 to keep your water
properly balanced. When TDS levels exceed 5,000ppm, it is recommended that you
subtract half of a tenth, or one twentieth of unit (.05) per 1,000ppm. And as
the TDS approaches that of seawater, the effect is negligible.
Hot tubs and spas
have a more significant problem with TDS levels than pools. Because the swimmer
load is relatively higher, more chemicals are added for superchlorination and
sudsing along with a higher concentration of bather wastes. The increased
electrical conductance that high TDS water promotes can also result in
electrolysis or galvanic corrosion. Every hot water pool operator should
consider a TDS analyzer as a standard piece of equipment.
A TDS analyzer is
required to balance the water of any pool or spa in the most precise way.
POOLPRO, ULTRAPEN™ PT1 and PoolMeter™ instantly display accurate TDS
levels giving you the information you need to ensure you
take corrective action before TDS gets out of hand.
is the last and least significant factor in maintaining water balance. As
temperature increases, the water balance tends to become more basic and scale
producing. Calcium carbonate becomes less soluble, causing it to precipitate out
of solution. As temperature drops, water becomes more corrosive.
In addition to helping determine water balance, temperature also affects bather comfort, evaporation, chlorination, and algae growth (warmer temperatures encourage growth). POOLPRO also precisely measures temperature to one tenth of a degree at the same time any other parameter is measured.
In the pool and spa industry, water balance is calculated using the Langelier Saturation Index (LSI):
SI= (pH + TF +
CF + AF ) – 12.1
PH = pH value
TF = 0.0117 X Temperature Value — 0.4116
CF = 0.4341 X ln(Hardness Value) — 0.3926
AF = 0.4341 X ln(Alkalinity Value) — 0.0074
The following is a general industry guideline for interpreting LSI values:
index between -0.5 and +0.5 is acceptable pool water.
index of more than +0.5 is scale-forming.
index below -0.5 is corrosive.
Alkalinity, and Calcium Hardness are the largest contributors to water
balance. Pool water will often be balanced if these factors are kept within the
The POOLPRO™ PS9 Titration Kit features an LSI function
that steps you through alkalinity & hardness titrations
and pH & temperature measurements to quickly and
accurately determine LSI. An LSI calculator allows you
to manipulate pH, alkalinity, hardness and temperature
values in the equation to determine water balance
adjustments on the spot.
The most immediate
concern of anyone monitoring and maintaining a pool is the effectiveness of the
sanitizer – the germ-killer. There are many types of sanitizers, the most common
being chlorine in swimming pools and bromine in hot tubs and spas. The
effectiveness of the sanitizer is directly related to the pH and, to a lesser
degree, the other factors influencing water balance.
To have true
chemical control, you need to monitor both the sanitizer residual and the pH and
use that information to chemically treat the water. To check chlorine residual, free
chlorine measurements are made. For automatic chlorine
dosing systems, ORP must also be monitored to ensure
Free Chlorine is the amount of chlorine available as
hypochlorous acid (HOCl-) and hypochlorite ion (OCl-),
the concentrations of which are directly dependent on pH
and temperature. pH is maintained at the level of greatest
concentration of HOCl- because hypochlorous acid is
a much more powerful sanitizer than hypochlorite ion.
Free chlorine testing is usually required before and after
opening of commercial pools. Samples should be taken
at various locations to ensure even distribution. Residual
levels are generally kept between 1-2 mg/L or ppm.
POOLPRO V.4.03 and later features the ability to measure
ppm free chlorine in pools and spas sanitized by
chlorine only. With this feature POOLPRO can measure
a dynamic range of chlorine concentrations wider than
that of a colorimetric test kit with a greater degree of
for Oxidation Reduction Potential (or REDOX) of the water and is
measured in millivolts (mV). The higher the ORP, the greater the killing power
of all sanitizers, not just free chlorine, in the water. ORP is the only
practical method available to monitor sanitizer effectiveness. Thus, every true
system of automatic chemical control depends on ORP to work.
The required ORP
for disinfection will vary slightly between disinfecting systems and is also
dependent on the basic water supply potential, which must be assessed and taken
into account when the control system is initialized. 650mV to 700 - 750mV is
generally considered ideal.
controllers can be inaccurate and inconsistent when confronted with certain
unique water qualities, so it is critical to perform manual testing with
separate instrumentation. For automatic control dosing, it is generally
recommended that you manually test pH and ORP prior to opening and then once
during the day to confirm automatic readings.
confirming automatic control dosing should be taken from a sample tap
strategically located on the return line as close as possible to the probes in
accordance with the manufacturer's instructions. If manual and automatic
readings consistently move further apart or closer together, you should
investigate the reason for the difference.
can only be obtained with an electronic instrument. Myron L®’s POOLPRO
and ULTRAPEN™ PT3 provide the fastest, most precise, easy-to-use method of obtaining ORP readings
to check the effectiveness of the sanitizer in any pool or spa. This is the best
way to determine how safe your water is at any given moment.
A relatively new
development, saltwater pools use regular salt, sodium chloride, to form chlorine
with an electrical current much in the same way liquid bleach is made. As
chlorine – the sanitizer – is made from the salt in the water, it is critical to
maintain the salt concentration at the appropriate levels to produce an
adequate level of sanitizer. It is even more important to test water parameters
frequently in these types of pools and spas, as saltwater does not have the
ability to respond adequately to shock loadings (superchlorination treatments).
chlorinators require a 2,500 – 3,000ppm salt concentration in the water (though
some may require as high as 5,000-7,000ppm). This can barely be tasted, but
provides enough salt for the system to produce the chlorine needed to sanitize
(It is important
to have a good stabilizer level – 30 - 50 ppm – in the pool, or the sunlight
will burn up the chlorine. Without it, the saltwater system may not be able to
keep up with the demand regardless of salt concentration.)
Taste and salt
shortages are of little concern to seawater systems that maintain an average of
32,000ppm. In these high-salt environments, you need to beware of corrosion to
system components that can distort salt level and other parameter readings.
incorrect salt concentration readings can occur in any saltwater system. The
monitoring/controlling components can and do fail or become scaled — sometimes
giving a false low salt reading. Thus, you must test manually for salt
concentration with separate instrumentation before adding salt.
You must also test
salt concentration manually with separate instrumentation to re-calibrate your
system. This is critical to system functioning and production of required
chlorine. Both the POOLPRO
and ULTRAPEN™ PT1 conveniently test for salt concentration at the press of the button as a check
against automatic controller systems that may have disabled equipment or need to
Though no one instrument or method can be used to
determine ALL of the factors that affect the comfort and
sanitation of pool and spa water, Myron L®’s POOLPRO
is a comprehensive water testing instrument that is
reliable durable, easy-to-use and easy-to-maintain and
calibrate. As a pool professional, a POOLPRO will not only
simplify your life, it will save you time and money.
– What to do with all those measurements
Data handling should be done
objectively and data recorded in a common format in the most
accurate way. Also, data should be stored in more than one permanent location
and made available for future analysis. Most municipalities require commercial
aquatic facilities to keep permanent records on site and available for inspection
at any time.
Myron L®’s POOLPRO
makes it easy to comply with record keeping requirements. The POOLPRO
is an objective means to test free chlorine, ORP, pH, TDS, temperature and the mineral/salt
content of any pool or spa. You just rinse and fill the cell cup by submerging
the waterproof unit and press the button of the parameter you wish to measure.
And model PS9TK features the added ability to perform in-cell conductometric titrations for Alkalinity, Hardness and LSI on the spot. Up to 100 date-time-stamped readings
can be stored in memory and then later transferred directly to a computer using
the bluDock™ accessory package. Simply pair the bluDock™ with your computer, then open the U2CI software application to download data. The user never
touches the data, reducing the potential for human error in
transcription. The data can then be imported into any program necessary for
record-keeping and analysis. The bluDock™ is a quick and easy way to
keep records that comply with governing standards.
NOTE: Consult your
governing bodies for specific testing, chemical concentrations, and all other
guidelines and requirements. The ranges suggested here are meant as general
Myron L® Company assumes no responsibility for lack of compliance to
specific regulations governing the testing and control of parameters in your
pool and/or spa.
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