Anyone and 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.

WATER BALANCE

Water is 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.

The pool 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.

Aggressive water 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 being basic.

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.
Myron L’s POOLPRO™ gives 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.

Total 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. MyronL’s Alkalinity Test Kit comes with sodium hydrogen sulphate tablets and a mixing/measuring vial to determine alkalinity in parts per million.

The other water balance parameter pool professionals are most familiar with is Calcium Hardness (CH). CH is 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 and has the least significant effect on the water balance when compared to pH and TA.

Total Dissolved 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. MyronL’s POOLPRO and POOLMETER™ immediately display TDS levels to correctly calculate your water’s saturation index and to ensure you take corrective action before TDS gets out of hand.

Temperature 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). MyronL’s POOLPRO also precisely measures temperature to one tenth of a degree at the same time any other parameter is measured.

The formula for determining water balance is called the Langlier Index, or Saturation Index. It is determined by the following formula:

SI= (pH + TF + CF + AF ) – 12.1

Where TF is the temperature, CF is Calcium Hardness, and AF is Total Alkalinity adjusted for temperature. 12.1 is the Total Dissolved Solids constant. Consult appropriate conversion charts to obtain the correct values for each variable.

pH, Total Alkalinity, and Calcium Hardness are the big three contributors to water balance. *Pool water will often be balanced if these factors are kept within the recommended ranges.