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Specialty chemicals reduce chlorine demand

By Marcelle Dibrell

2021 has been a rough year for pool and spa professionals attempting to get their hands on the products necessary to keep pools and spas looking their best.

Increased demand and reduced supply resulted in the great chlorine shortage of 2021, which led to panic-purchasing, hoarding, and price increases.

Thanks to the coronavirus pandemic, household cleaning product manufacturers were already working at capacity trying to keep up with demand before a hurricane took at a major chlorine factory and a third of the country’s supply. With new pool construction at an all-time high (up by nearly 24 percent), combined with the nation’s pools opening earlier and closing later in the year, chlorine consumption has been unprecedented.

It has all meant that service technicians have been forced to get a little creative when it comes to keeping their customers’ pools and spas sparkling and clear.

Many have turned to select specialty chemicals to supplement the two-fold job that chlorine performs.

According to the 2020 Pool and Hot Tub Alliance Market Report, the market share of sales of specialty chemicals grew by one percentage point from 2019 to 2020. It seems likely that this growth reflected a need to complement chlorine’s special purposes.

And it makes sense to use specialty chemicals if you understand exactly what chlorine does in a pool. It comes down to the two main categories of chlorine demand: the need to control living contaminant growth and reproduction, and the removal of non-living oxidants. Minimizing chlorine use is possible if you can find a way to minimize the chlorine demand.

In terms of controlling living contaminant growth, we are primarily trying to mitigate the growth of harmful bacteria and germs – pathogens that can make people sick. Although it does not take many harmful pathogens to cause a recreational water illness, fortunately, these germs are destroyed with just a small amount of chlorine. But the primary living contaminants that consume chlorine are algae, and algae comes in thousands of varieties that, given the proper nutrients and conditions, can reproduce rapidly in a pool or spa. So, it’s about ensuring that the kill rate of chlorine exceeds the reproduction and growth rate of algae, and this can be achieved with a few select specialty chemicals.

One way of maximizing chlorine’s kill rate is through controlling the cyanuric acid concentration. Because the killing form of chlorine – that is, hypochlorous acid – is proportional to the cyanuric acid, if we keep cyanuric acid down to the minimum amount needed to protect chlorine from the sun, then chlorine’s efficacy against algae can be maximized. Regular use of chlorinated cyanurates such as trichlor tabs and dichlor will result in cyanuric acid levels quickly spiking out of control. A service tech’s options to reduce cyanuric acid are twofold: either drain and refill the pool, or use a specialty chemical to chemically remove the cyanuric acid.

But another method of getting chlorine’s kill rate to out-perform algae’s growth rate is to try to slow the algae growth.

This can also be accomplished through specialty chemicals. Algicides and algistats are obvious ways to control algae, but what about removing the conditions that favor algae growth?

If a primary source of algae food – that is, phosphates – is removed, algae have a much more difficult time getting a toehold, so phosphate removers can make a real difference.

The other method of reducing chlorine demand is by removing the other source of that demand – the non-living oxidants. In a pool, those non-living oxidants come in three main categories that include metals, nitrogen compounds, and non-living, carbon-based bather waste.

In swimming pools, chlorine reacts with these items by oxidizing them, so if their presence can be reduced, chlorine demand will naturally go down. Fortunately, there are certain specialty chemicals that can reduce some of oxidants.

In this issue of Service Industry News, we’ll take a closer look at some of the popular specialty chemicals used today, and how they can reduce chlorine use, in a time when there has never been such strong demand.

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