By Alicia Stephens
To fully understand saltwater pool chemistry one must start by separating fact from fiction, as many misconceptions stem from a lack of knowledge. The most common misunderstanding about saltwater pools is they are fundamentally different and do not use chlorine as a sanitizer.
In reality, saltwater pools use a special process to create free available chlorine (FAC), but require similar products to maintain water quality. It is true, weekly maintenance for saltwater pools does not have to be difficult and they may not require as much time to maintain as a traditional halogen (chlorine [Cl], bromine [Br]) pool, but they are not maintenance-free. In fact, one of the primary reasons the water quality is so much easier to maintain is because chlorine is consistently produced as a sanitizer.
Saltwater pools experience many of the same problems that befall traditional pools, which use chlorine as the primary sanitizer, but there are fewer issues that require attention because of the unique way the sanitizer is produced. This includes balancing the pH, maintaining a chlorine residual, solving cloudy water and surface problems, battling algae, and preventing scale. Each of these potential issues can be frustrating for a pool owner, but can be prevented with proper maintenance.
The importance of pH
As many pool technicians know, pH is a key water balance parameter. Almost anything that comes into contact with the water has the potential to impact the pH—even the products that are routinely used to help maintain the water can influence how the pH behaves.
In the process of generating chlorine in saltwater pools, the water’s pH increases over time. This is a result of the byproducts that are created when salt is turned into free available chlorine.
Pass the salt
Salt is the first thing that is needed to produce chlorine in a saltwater pool. It can be added using any number of pool salt products available. Keep in mind, some alternative sources of salt that are not made for the pool environment may contain impurities such as iron (Fe), which can eventually cause surface issues.
The reaction that produces free chlorine, or hypochlorous acid (HClO), occurs within the electrolytic cell, commonly known as the chlorine generator. As chloride ions pass through the cell over the plates, chlorine gas is created through the process of electrolysis.
The chlorine gas created from the electrolysis of salt reacts with the water to form hypochlorous acid. This is why saltwater pools are, in fact, chlorine pools. The active sanitizer is not any different than the end result of adding chlorinating tablets, sticks, granular chlorine, or liquid chlorine. They all form hypochlorous acid. Ultimately, saltwater chlorine generation is just another method to chlorinate a pool.
Sodium hydroxide (NaOH) is also produced during this chemical reaction, which has a pH of 13.5. It is this byproduct of electrolytic chlorine generation that is responsible for the troublesome and steady increase in pH experienced in saltwater pools.
As a result, saltwater pools require routine pH adjustment. A weekly application of a pH decreaser product is a necessity for pools using a chlorine generator. Without it, many problems can occur as pH continues to rise in the pool. If left unchecked, high pH can lead to multiple problems in the pool environment, including ineffective sanitizer, cloudy water, scaling, and algae.
Failure to maintain
During the season, another issue saltwater pools may experience is failure to maintain a free chlorine residual. This is also a common issue in traditional halogen pools, but in saltwater pools this problem can be typically tracked down to one of two causes. First, the pool is experiencing a chlorine demand, or second, the cell is no longer capable of producing enough free chlorine.