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Pool Rangers, Inc
WATER CHEMISTRY
WATER CHEMISTRY FROM TAYLOR TECHNOLOGIES
At Pool Rangers, Inc. we believe in educating our customers for those who want to have a better understanding of their pool and what it is that we are doing to it.
Service technicians who have had long experience with pools are acutely aware of the damage that water can cause when in contact with concrete grouting, marsite, and metals (e.g., steel, copper). Water can either corrode such surfaces or deposit a white film or crusty, coarse substances called scale. Water that corrodes and/or is scale forming is called unbalanced water while water that causes no damage is balanced.
Corrosive water is “aggressive” and attempts to dissolve concrete and metals, pitting concrete and destroying steel filters and copper heat exchangers. A tell-tale sign of corrosive water is staining, which is the deposit on the pool’s surface of colored metal salts of iron (brown) or copper (blue/green/grey/black). Scaling water does the opposite – it attempts to deposit or precipitate calcium carbonate out of solution, causing a white film or rough, unsightly deposits on pool surfaces, and possibly plugging the filter and circulation piping. Water that is balanced exhibits none of these damaging properties.
The obvious goal is to keep pool water in balance to avoid unnecessary and costly repairs. Such a task is accomplished by controlling the factors or parameters that determine water balance: pH, calcium hardness, total alkalinity, temperature, and total dissolved solids (TDS). In general, temperature and TDS have a minor influence on water balance.
Total Alkalinity
Ideal range: 80 – 120 ppm
Total Alkalinity is the measure of the ability of water to resist changes in pH…that is…the ability to “buffer” water from wide pH swings. Essentially the amount of sodium bicarbonate dissolved in pool water, total alkalinity serves two purposes: it is the governor of pH and it is the third and last major factor that affects water balance.
A buffer is a chemical system that resists change upon the addition of acids or bases. In water that contains no buffering ability, pH can wander dramatically. This is called pH bounce – a rapid fluctuation of pH levels with the addition of small amounts of acid, base (alkali), or other pH altering agents. The result is highly unbalanced water resulting in damage to light rings, stainless steel ladders, copper heat exchangers, and concrete pool surfaces.
Low Total Alkalinity:
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corrosive water
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pitting of concrete
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metals dissolve
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surface staining
Non-Balance Problems
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pH bounce
High Total Alkalinity:
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scaling water
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white film/crusty deposits
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plugged filters
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reduced circulation
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cloudy pool
Non-Balance Problems
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pH drifts upward
PH
Ideal range: 7.4 – 7.6 ppm
A scale of measurement, pH was invented to measure the acidity of water in the brewing of beer in the early 1900s. pH stands for potens hydrogen, Latin for “hydrogen power,” as acidity is caused by a predominance of the chemical species H+ or hydrogen ion.
pH is measured on a scale from 0 – 14, with a pH of 7 being neutral. Below 7, the water is acidic and above, the water is alkaline (“basic”). The pH scale is logarithmic, meaning that every whole unit increase is 10 times its predecessor. Therefore, a pH of 6 is 10 times more acidic than a pH of 7 and a pH of 3 is 10,000 times more acidic than a pH of 7!
Note that the pH range recommended for pool/spa waters is slightly alkaline, which promotes bather comfort, as the pH of the human eye is about 7.5.
Low pH:
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corrosive water
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pitting of concrete
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metals dissolve
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surface staining
Non-Balance Problems
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chlorine loss
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vinyl wrinkles
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skin/eye irritation
High pH:
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scaling water
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white film/crusty deposits
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plugged filters
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reduced circulation
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cloudy pool
Non-Balance Problems
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chlorine inefficiency
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skin/eye irritation
Chlorine Chemistry
Ideal range: 2 – 4 ppm
Sanitation is the reduction of the level of microorganisms (living cells so small they can only be observed through a microscope) by significant numbers (usually 99.9% or more) to safe levels as established by state or federal authorities.
Sanitizer is the chemical or device that kills or inactivates the microorganisms present in pool/spa water. Chlorine, followed by bromine, are the most popular choices. Other sanitizers include ozone, biguanide (PHMB), copper/silver ionization, and UV radiation.
Defined as a sanitizer, chlorine destroys microorganisms; however, it carries out an additional function as an oxidizer. This oxidation is the “burning up” of organic contaminants introduced to the water by the bather (e.g., hair gels, deodorant, suntan lotion, body oils, perspiration, etc.) and the environment (e.g., pollen and dirt). Studies have shown that only 10% of chlorine is needed for sanitation while 90% of chlorine is used for oxidation.
Microorganisms and organics consume chlorine. This consumption is called the chlorine demand and is defined as the amount of chlorine that will react with contaminants before any chlorine is left unreacted.
THE CAUSE OF CHLORINE DEMAND
Microorganisms are living creatures too small to be seen by the naked eye and are constantly introduced into the pool by rain, wind, and the human bather. Algae, bacteria, fungi, protozoans, yeasts, and viruses are the kinds of organisms of concern. Most organisms are harmless to the human body but others are disease- and infection-causing. If not killed, these “germs” are transmitted via water to other bathers.
Non-living organic contaminants are also objectionable. An active adult swimmer can lose a pint of perspiration or more per hour. Perspiration is loaded with compounds resembling the chemistry of urine. The body is also constantly shedding microscopic skin particles sloughed off by the friction of water. These are all “involuntary wastes.” Add in “voluntary wastes” such as expectorate, nasal discharge, fecal matter, and urine and you begin to appreciate the bather load created.
Organics cause pool water to become dull, listless, and cloudy. Periodic addition of an oxidizing chemical (called shocking, or superchlorinating specifically when chlorine is used as the oxidizer) will rid water of these contaminants, leaving it sparkling and inviting.
Chlorine Stabilization
Ideal range: 60 – 80 ppm
In 1958, cyanuric acid (a week acid often abbreviated CYA) was discovered to inhibit chlorine depletion by sunlight. In other words, cyanuric acid stabilized the free chlorine residual from sunlight destruction. When CYA is dissolved in water at 25 ppm, FC (free chlorine) lasts three to five times longer than pool water not containing CYA. Above 50 ppm, only marginal stabilization benefit is observed. Note: Cyanuric acid stabilizes hypochlorous acid Regardless of the form of chlorine used!
Cyanuric acid is an odorless, white granular substance. It is also known by such names as stabilizer, isocyanuric acid, conditioner and CYA. When dissolved in pool water, FC residuals last three to five times longer in the presence of sunlight.
OVERSTABILIZATION
Although cyanuric acid possesses all these benefits, it also has a significant downside. In the process of stabilizing FC, cyanuric acid causes the chlorine to slow down or become less effective both as an oxidizer and a sanitizer. This must be compensated for by using a higher concentration of chlorine in the pool.
STABILIZED CHLORINES
In 1958, two new products for pool water sanitation were introduced. Called chlorinated isocyanurates, or simply “isos,” they are sanitizer and stabilizer all in one. The key to understanding the stabilized chlorines “trichlor” and “dichlor” is that their chlorine is attached to a CYA molecule. Unstabilized chlorines – chlorine gas and sodium, calcium, and lithium hypochlorites – do not have a CYA component. Outdoor pools sanitized with unstabilized chlorine must have CYA added seperately.
Although this one-step process has made isos very popular, operators need to be aware that CYA can build up unintentionally to an objectionable level. This is because after the chlorine part of an iso compound has been depleted, the cyanuric acid component remains behind, dissolved in the water. CYA can accumulate faster than splash-out, carry-out, and backwashing removes it. For this reason, better test kits allow you to monitor CYA.
Calcium Hardness
Ideal range: 200 – 400 ppm
Water that contains little or no calcium or magnesium is called soft. Water that contains high levels of calcium and magnesium salts is called hard as it consumes soap and makes it “hard” to form suds. In wash water the minerals combine with soap to form a grey insoluble curd-like scum, making cleaning less effective yet more expensive. With the advent of synthetic detergents, this problem has improved; however, for home and some industrial processes, hard water is often “softened” before use by water softeners that remove all of these minerals.
In laundry applications, the goal is to remove calcium/magnesium from water. In pools, magnesium does not form scale and interest is focused only on calcium. Pools having too much calcium may scale, but pool water entirely deprived of calcium becomes aggressive and seeks to dissolve calcium into the water from contact surfaces, such as grouting or concrete. High hardness can be reduced by partially draining the pool and refilling with fresh water of lower hardness.
THE EFFECTS OF HIGH AND LOW HARDNESS
Specifically, water with high calcium hardness gets cloudy unless the alkalinity and/or pH are low enough to compensate. As mentioned, the excess calcium carbonate will precipitate as crusty, grayish white scale on surfaces, piping, and equipment. It’s unsightly, can cause abrasions on users and snag bathing suits, and makes a good anchor for microorganisms. It will clog filters. When it builds up in piping, circulation is reduced and pressure increases. Scaling is an especially acute problem in heaters because calcium’s solubility is inversely proportional to temperature: as temperature increases, less calcium is able to stay dissolved. Scale on the pipes or coils acts as an insulator, slowing heat transfer. This makes it more expensive to heat the water. Over time, thick scale will cause a heater to fail.
Water with low calcium hardness will seek more by dissolving it from surfaces it comes in contact with that contain calcium, such as plaster, grout, and concrete decking. The late Dr. Neil Lowry, a well respected instructor in our industry, preferred to call water with low calcium hardness “aggressive” rather than “corrosive” because the latter term implies the destruction of metals. He would point out that copper water pipes in homes equipped with water softeners last for decades! The corrosiveness of unbalanced water, he would tell his students, comes from poorly maintained alkalinity and pH.
Low Calcium Hardness:
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corrosive water etching of plaster
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pitting of concrete
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dissolving of grout
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pitting of pool decks
High Calcium Hardness:
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scaling water
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white film/crusty deposits
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plugged filters
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reduced circulation
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cloudy pool
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heater inefficiency