April 1, 2015
By Claudio Azurmendi
The difference between owning a pool with a salt system and one that uses traditional means of sanitation may seem expansive. For many, the perception of salt pools is that they are maintenance-free and often times chlorine-free systems. Dispelling the myths about salt pools can be difficult, but as pool professionals there is a necessity to at least massage pool owner’s perceptions regarding salt pool maintenance and ownership. By dislodging the misconceptions about salt pools, service professionals will be able to lengthen the life of their customers’ pools and keep them sparkling throughout the summer.
The first step in tackling the differences and similarities between each pool type is to understand how salt pools actually work. No matter the salt pool cell or chlorinator manufacturer, all systems use an electrolytic chlorine generator (ECG). The inner hardware usually comprises titanium (Ti) plates that are coated with ruthenium (Ru) and/or other rare earth metals. These systems carry out the process of electrolysis whereby the chloride ion (from salt) is converted to chlorine gas (Cl2) by passing an electric current through saltwater.
When applied to water, chlorine gas immediately converts to hypochlorous acid (HOCl). The other byproducts of electrolysis of the chloride ion to hypochlorous acid are hydrogen gas (H2) and sodium hydroxide (NaOH). Hydrogen gas releases harmlessly into the atmosphere (the effects of the sodium hydroxide ion will be addressed later in the article). This brief summary of chlorine production via ECG in salt pools may not be news to readers; however, one of the most common misconceptions about saltwater pools is they are not chlorine pools. Politely educating salt pool owners on this point will go a long way towards properly maintaining their water. Once they realize adding more salt is not a cure-all, it will help steer these pool owner towards proper maintenance and treatment options such as supplemental shocking, scale inhibitors, and pH balancers.
Most ECGs handle routine chlorination along with weekly shocking with ease. Consumer salt chlorine generators running at 100 per cent output typically produce anywhere from 0.3 to 0.9 kg (0.7 to 2.0 lbs) of chlorine—assuming the ECG is operating at 100 per cent output, or on a ‘boost’ setting for 24 hours a day. During periods of heavy usage, rain or weather extremes, the chlorine output capacity of an ECG can be strained. Just like any other pool, an occasional oxidizer supplement outside of routine chlorination methods may be necessary.
Salt pool owners may balk at the idea of adding chemicals to their pools, but occasionally, the boost on their ECG may need a boost of its own. Granulated dichloro- and trichloro- isocyanurate-based shocks can be used as maintenance products after events such as pool parties, rain storms, and other inclement weather. These shocks provide a quick boost of chlorine without significantly impacting pH balance or calcium hardness levels, which is especially important for salt pools. Regular use of chlorine shocks in salt pools helps prolong the life of the ECG by cutting down on cell usage rates. Much like a traditional chlorine pool, salt pools will occasionally encounter chlorine demand. When the demand outpaces the capabilities of the ECG, which is possible for even a modest chlorine demand, the best way to treat this is by applying chlorine shocks. If a salt pool owner is reluctant to throw granular chlorine shocks into their ‘chemical-free’ pool for maintenance after rain storms or heavy usage, monopersulfate-based products, or chlorine-free oxidizers, are other viable alternatives.
Although chlorine shocks must be used when treating a chlorine demand, monopersulfate products oxidize contaminants and help clear cloudy water, much like chlorine-based shocks. Whether using monopersulfate treatments or chlorine shocks, regular use of supplemental oxidizers ultimately leads to better water quality and extends the life of the ECG.
Many problems can be avoided if proper chlorine residuals are maintained at all times. Supplemental chlorination/oxidation helps a salt system avoid dipping below recommended chlorine residuals. Another way to get the most out of an ECG is by maintaining a stabilizer residual.
Cyanuric acid (CNOH)3, commonly referred to as stabilizer or conditioner, increases the stability of chlorine against the sun’s ultraviolet (UV) rays. Chlorine dissipates quickly, especially during summer months, unless it is protected by some outside source. The chlorine manufactured by an ECG is just as susceptible to UV degradation as chlorine from a tab, stick, or granule. Stabilizer allows a salt pool owner to run their ECG less often or at lower output, thus extending the life of the cell. In addition to using stabilizer, the use of regular scale inhibitors and proper pH maintenance can also prolong the cell life.
Before delving into scale inhibitors, it is now necessary to turn back to the problem of sodium hydroxide. Keep in mind, chlorine manufactured within the ECG has byproducts. For example, while generating hypochlorous acid, they also produce sodium hydroxide, which is a strong base (i.e., it dissociates completely in solution becoming a strong electrolyte), which raises pH and can be harmful to the overall lifespan of not only the ECG cell, but also other equipment and pool surfaces. Water becomes corrosive when pH is too low, and scaling when the pH is too high—especially for areas with hard water. In this case, it is necessary to keep pH within a certain range, typically 7.4 to 7.6, to avoid calcium carbonate (CaCO3) precipitation on surfaces, otherwise known as scale. The high localized concentration of sodium hydroxide at the ECG’s cell plates during chlorine production results in a high pH. Thus, the outcome is a scale prone environment.
Two water treatment methods can help counter the effects of rising pH in salt pools: scale inhibitors and pH decreasers.
Over time, scale accumulates on the cell plates as a result of the cell’s high scaling conditions. As accumulation proliferates, also known as fouling, the electric current passing between the ECG plates for chlorine production is impeded and eventually comes to a halt. To help combat this phenomenon, most ECG’s have a reverse polarity function, which changes the direction of the electric current within the cell, purging accumulated scale from the plates.
Further, cell acid cleaning can also alleviate the inevitable stunted chlorine production of the cell. However, like a favourite T-shirt that gets washed over and over, leaving behind a tattered rag, the cell will eventually lose its protective coating with more and more acid cleanings leading to equipment failure. To maintain the longevity of the cell, the best practice would be to use a treatment which prevents scale accumulation from forming on the cell plates altogether—right? Wrong. Although this seems like the practical answer to maintaining a long-lasting ECG, unfortunately, it is not that simple. Even with reverse polarity functionality and acid cleanings, over time ECG plates will accumulate scale regardless of the treatment used. Scale inhibitors can be used, however, to slowdown the process of cell fouling.
In doing this, the frequency of abrasive cell acid cleaning can be reduced, thus improving the cell’s lifespan. Different scale inhibitors will have varied functionality and stability in salt pool environments. Polymer-based scale inhibitors typically provide a useful blend of performance and stability within the harsh environment of an ECG.
Sodium hydroxide production is one of the reasons why the ECG environment is so harsh. While operating, the ECG essentially produces pH increaser leading to constant pH rise in salt pools. Depending on pump runtime and the chlorine output settings, the ECG will gradually push the pH up. Therefore, like any other pool, salt pools require the pH to be monitored and adjusted for proper balance. Basic water balancing steps can be taken to fight pH rise in salt pools with the principal agent of treatment being sodium bisulfate (NaHSO4)-based pH decreaser. Sodium bisulfate not only decreases pH, but since it is a granular product, it is also much easier to handle than liquid pH decreasers. Checking pH balance weekly, and after heavy-cell usage, will help establish when and how much pH decreaser should be applied.
For most salt pools, weekly applications of pH decreaser are going to be the best way to counter pH rise. There are numerous benefits to maintaining proper pH: chlorine is going to be more effective at killing bacteria; bathers will be more comfortable; and pool surfaces and equipment such as heaters and ECG’s will be better protected against scale accumulation. Maintaining the cell and chlorine output through use of stabilizer, scale inhibitors, pH decreasers, and supplemental oxidation extends the life of valuable pool equipment, including the ECG.
Typical pool problems such as cloudy water and algae blooms can occur in salt pools just like any other pool. Salt pool owners may try adding more salt to their pool to no avail or turning their ECG to boost for a couple days, but in some instances, running the cell on boost will not be enough.
Re-emphasizing one of the important themes of salt pool treatment, salt pools are chlorine pools and may need help from outside sources when it comes to water quality problems (e.g. algae blooms) or heavy usage.
Most algaecides are compatible with salt pools including quat, polyquat, or copper-based algaecides. Using a chelated-copper, or non-staining algaecide is particularly important for salt pools. Localized high pH within the ECG can precipitate copper (Cu) leading to water discolouration or staining. When copper is chelated, it is unlikely to cause staining and water discolouration. In addition to algaecides, many products or remedies used in traditional chlorine pools may be used in salt pools.
Clarifiers, flocculents, filter aids, phosphate removers, and enzyme products can all be used in salt pools if an owner would like the water to look more polished or needs to remedy cloudy water. Phosphate (PO43−) removers can be particularly useful in salt pools. Calcium phosphate, like calcium carbonate, can accumulate on pool surfaces and the plates of an ECG as scale. When phosphate is removed from the water, the likelihood of this type of scale formation dissipates dramatically. Depending on the type of algaecide or other ancillary product employed, it may be necessary to top off scale inhibitors after treatment.
Owners of salt pools, like any other pool owner, take great pride in their backyard oasis. Therefore, it is beneficial for salt pool owners and service professionals to consider the fine details and precautions that should be adhered to when maintaining them. Ideally, no additional chemicals or maintenance would be necessary for salt pool owners. But, to protect their investment, salt pool owners need to be coached on how similar their pool is to a traditional chlorine pool. Educating salt pool owners on the benefits of implementing the likes of stabilizers, scale inhibitors, supplemental oxidizers, and pH decreasers into their maintenance and treatment programs can lead to increased longevity of their salt chlorine generator and ultimately a more enjoyable pool owning experience.
Claudio Azurmendi was a product development chemist for BioLab Inc., A KIK Custom Products Company. He received his bachelor of science in chemistry from Georgia State University and joined BioLab in 2009 as a customer care technical solutions specialist. He moved to the technical services department in 2010, then on to the Research & Development group in 2013. Claudio passed away in 2014. He was a talented chemist and a respected member of the product development team. His legacy is the on-going contribution his work provides to BioLab and to the pool and spa industry.
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