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Testing pool water is a balancing act

By Marcelle Dibrell

Water can be a dangerous substance when it is not properly managed.

Left to its own devices, water can harbor a host of threatening pathogens, capable of causing sickness and even death, as some of the articles within this issue of Service Industry News can attest.

There’s e. Coli, Legionella, giardia, cryptosporidium, and a variety of other disease-causing agents that it is part of the job of the service professional to prevent by using a measured quantity of disinfectant.

Indeed, among the most important jobs a service tech has is a basic knowledge about the sanitizer levels in all the pools on a service route.

And that means more than adding a gallon of chlorine if the water looks a little cloudy, or spending 15 minutes to simply skim the surface if the water looks clear.

No, the only way to know that the water is safe is to test.

But ensuring bather safety is just one aspect of the job entrusted to the pool and spa service professional.

Protecting customers’ valuable outdoor investments is the other critical part of the job, because there is another reason why water can be a dangerous substance when it’s not properly managed.

Known as the “universal solvent,” water is capable of leaching materials right out of pool surfaces, undermining the integrity of what is meant to be a water-tight vessel.

But what truly governs water’s solubility properties is water balance.

Water balance comes down to a handful of factors that dictate whether or not the pool is self-destructive.

Those five factors are pH, alkalinity, calcium hardness, temperature, and to a small extent, total dissolved solids. Taken together, these control the long-term viability and aesthetic please-ability of every pool that was ever created.

Not balanced, water can become scale forming, where it precipitates calcium carbonate out of solution, depositing it on surfaces, like tile lines, heaters, and salt cells. Alternately, water can become aggressive, dissolving concrete and metals, leading to etching and stained surfaces. Water balance really matters.

And the only way to know that the water is balanced is to test.

In the pool and spa industry, water balance is determined by the Langelier Saturation Index, or LSI. The LSI takes the contributions of those five factors together mathematically to provide a practical way of indicating balance. Large positive numbers are bad; large negative numbers are bad. With the LSI, the math is simple: The magic number is zero.

Large negative LSI numbers can mean etched pool plaster and corroded metal parts in the heater, pump, and filter. It is damaging to both vinyl lined and fiberglass pools, stretching the vinyl or blistering the fiberglass. It also can cause bather discomfort through skin and eye irritation.

But large positive LSI numbers are nearly as problematic, most notably leading to scale formation. And beyond being unsightly, scale disrupts heater and salt cell operations, reducing efficiency at best, and halting all operations at worst. High LSI also causes cloudy water, metallic stains, and shortens filter runs.

It isn’t hard to calculate the LSI — a fairly simple formula is used that is familiar to many service professionals.

Nowadays, however, with the modern technology of smart phone apps, who needs to drag out pencil, paper, and conversion factor charts? As easy as it is to calculate, it’s easier still, not to mention faster, to simply plug the tested water balance parameters into any of a number of free apps, and let your phone do the work.

But to obtain those water balance parameters, the pool still needs to be tested, which is the subject of this particular issue of Service Industry News.

Special acknowledgement is given to the Association of Pool and Spa Professionals Fact Sheet, “Common Interferences in Pool and Spa Water Testing,” where some of the information contained in accompanying articles can be found.

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