Clean and clear pool water does not have to be a surprise

by brittney_cutler_2 | October 22, 2021 9:00 am

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By Kevin Vlietstra

Shocking the pool is a water treatment process every pool owner and service professional has done. Some homeowners who have done it before (whether themselves or had a service professional do it) probably know it needs to be done again. This article not only answers the question of why it needs to be done, but also explains why it is important to do come closing season.

Due for a shock

A daily oxidizer (typically chlorine or bromine) needs to be added to pool water to kill and inactive germs, bacteria, algae, and other pathogens. For the average pool, this level is a super low amount of two to four parts per million (ppm); for spas the level is a touch higher at three to five ppm. If this was all one needed to do to take care of their water, then pool maintenance would be super easy. That said, upkeep is easy for a commercial pool with feed pumps and monitoring systems; however, that is beyond the scope of this article. This article will focus on residential pools and those who aid in their upkeep.

The reality is pools are going to be used and, when they are, a slew of new contaminants and wastes are then introduced into the water. The moment these added wastes are introduced into the pool, the water’s oxidizing agent immediately starts to go after these wastes. On top of the mere introduction of these wastes, oxidizing agents will remove them at different rates. For example, 59 mL (2 oz) of sweat is going to breakdown quicker than the same volume of urine.

As the pool continues to be used, pool and air temperatures rise and, as the contaminant load from the pool being outdoors increases, the oxidizer can get quickly overwhelmed. Once the oxidizer (again, typically chlorine) level declines, the pool becomes open to the common unwanted water conditions such as algae or fungal growth or cloudy and smelly water.

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Culture shock

Shocking (often called oxidation, the terms are often used interchangeably), in relation to recreational water care, is the cleaning of water chemically. In other words, shocking is performed to scour the water of bather wastes, outside contaminants, and more. Those contaminants could lead to poor water quality but could also lead to the formation of combined chlorine (chloramine), which may require more shock to remove from the pool.

For many who take care of recreational water, their go to when performing this type of water cleansing is to add a chemical that contains chlorine. Chlorinating shocks are good choices because not only an oxidizer is being added to the water, but also a sanitizer which will knock down bacteria and algae counts.

The downfall of chlorinated shocks is they lack the ability to remove organic chloramines quickly, and frequent and repeated shock treatments can lead to the formation of undesirable disinfection byproducts.

Another option is using a shock without chlorine. Keep in mind, when using a chlorine-free shock no sanitizer being introduced to the water. Since there is a lack of a sanitizer, it is a poor choice for solving more technical or complicated problems such as algae outbreaks.

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In any event, chlorine-free oxidizers perform a more thorough removal of wastes, which more than makes up for what it cannot do. Additionally, a negative charge to the contaminants allows filters to quickly remove what is not broken down in the water resulting in clearer water.

Though shocking pool water is a necessity for water care maintenance, the frequency of when it needs to be performed can be changed up with the use of other products and system supplements.  Enzyme treatments is one such aid as it breaks down complicated waste structures in the water.  Having a net result of leaving the oxidizer to perform more effectively means less chemicals are needed overall.

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Ozone, ultraviolet (UV), and other advanced oxidation processes (AOP) also breakdown and remove unwanted wastes and contaminants from the water. The addition of these secondary systems will help to limit the amount of oxidizer needed to be applied to the water. However, time is needed for these systems to perform, and sometimes time is scarce, or the water quality falls behind and the pool needs to be cleansed with shock.

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Mould, algae, bacteria, viruses, and other micro-organisms all linger in the pool regardless of which season it is. Add heat, such as the case with hot tubs and spas, then all those water contaminants start to grow and multiply, which then puts a demand on the amount of oxidizer needed. Sticking with spas, another element of note that is added sometimes in droves to hot tubs and swim spas is sweat. Hot tubs typically have a water temperature higher than the average body temperature, so the body is naturally going to sweat to help cool itself. Swim spas should be thought of as a little athletic area. When someone is using a swim spa, it should be imagined that a high intensity workout will occur, which leads the body to perspire. In all aspects, these vessels will require more oxidizers than pools, relative to their size.

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The inverse of heat is cold, and as water temperatures decrease the activity of these lingering waterborne growths and pathogens also decrease. When growth and activity decreases, the overall need for oxidizers lessens as well. Just like when the pool is open, when it is closed there is equal importance in reducing and eliminating these precursors to water issues or at least keeping them under control.

Lessen the shock upon pool opening

When the season winds down, shocking the pool water is a must to reduce the number of contaminants. After the water is shocked, contaminant loads are reduced which frees up the disinfectant (sanitizer) to help control the other materials lingering in the water—either currently or other contaminants that may get into the pool during the off-season.

There are two different camps in what works best. On one end, there are those who like to use chlorinated products, while on the other, there are those using non-chlorine oxidizing shocks.

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Using chlorinating products to close a pool has its advantages. If chlorine levels are non-existent then administering a chlorinating shock will simultaneously scourer the pool of algae, bacteria, and other contaminants, while leaving a lingering amount of chlorine for the closing period. When unstabilized chlorines are used, the impact to the water’s pH is minimized.

Non-chlorine oxidizing shocks, relative to chlorine, is still an up and comer in the recreational water maintenance industry. Since most are comfortable with chlorine’s abilities, most do not look at non-chlorine as an effective tool—especially when it comes to closing a pool. However, just because the product does not have chlorine present does not make it any less of an oxidizer.

Non-chlorine oxidizers can scour more contaminants in the water than its chlorine predecessor. And since it does not contain any chlorine, it will not interact with chlorine and possibly form any disinfection byproducts. Most importantly, its lack of chlorine is better for the long-term appearance of the pool’s surface. Regardless of its effectiveness as an oxidizer, a chlorine presence during the off-season is still a must.

Kevin Vlietstra is the technical director and regulatory specialist with Haviland Pool and Spa Products. He has been working in the recreational water industry for more than 20 years. He can be reached via email at kevinv@havilandusa.com.

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