The widely held belief that salt itself sanitizes a pool is a misunderstanding rooted in the success of modern saltwater systems. Algae, a common issue for pool owners, is a simple plant-like organism whose growth is fueled by sunlight, warm water, and nutrient imbalances. Salt (sodium chloride) does not act as a direct algicide in the concentrations found in a typical residential pool. The actual agent that eliminates algae and keeps the water clear is the chlorine that the system continuously generates.
The Chemical Distinction: Salt vs. Sanitization
The salt added to a pool is merely a source ingredient, not the active defense against contaminants like algae. A saltwater pool maintains a salinity level typically between 2,700 and 3,400 parts per million (ppm). This is less than one-tenth the salinity of the ocean, which is closer to 35,000 ppm.
Algae are highly adaptive organisms. For salt to kill algae through osmosis—the process of drawing water out of the cell—the pool would require a far higher concentration. This hyper-saline environment would be necessary to overcome the algae’s natural ability to regulate its internal water pressure. Freshwater algae, the primary culprits in residential pools, often require salinity levels exceeding 20,000 ppm for significant growth reduction.
Therefore, the salt concentration maintained for a comfortable swim and optimal equipment function is biologically insignificant to the algae. The salt in the water is a precursor, waiting to be chemically converted into a potent sanitizer.
How Saltwater Systems Prevent Algae Growth
Algae control in a saltwater pool is achieved entirely by the presence of a Saltwater Chlorine Generator (SWCG). This device uses a process called electrolysis to convert the dissolved sodium chloride (NaCl) into chlorine. When the salt water passes over the generator’s cell plates, a low-voltage electrical current splits the salt molecules.
This reaction produces hypochlorous acid (HOCl), the strong sanitizer found in traditional chlorine products. Hypochlorous acid actively oxidizes and destroys algae cells, bacteria, and other organic matter. After the hypochlorous acid completes its sanitizing work, it reverts back into salt, and the cycle repeats when the water passes through the cell again.
The effectiveness of this system against algae stems from its ability to provide a continuous, low-level flow of sanitizer. This steady production maintains a constant chlorine residual, preventing algae spores from taking hold and multiplying. Traditional chlorine pools rely on periodic manual additions or “shocking,” which can sometimes result in temporary dips in sanitation levels that allow algae to bloom. The automated, consistent nature of the SWCG makes it a highly effective tool for preventing algae growth.
The Negative Impact of Excessive Salinity
While salt is necessary for the generator to function, adding an excessive amount of it to the pool will not improve algae control and can instead lead to damage. If the salinity level rises significantly higher than the recommended range, such as above 5,000 ppm, it creates a chemically aggressive environment. This elevated concentration of total dissolved solids (TDS) accelerates the corrosive process on metal components.
High salinity can cause damage to pool equipment, including heaters, handrails, and ladder anchors. Furthermore, when highly saline water splashes out and evaporates, it leaves behind pure, solid salt crystals on surfaces like porous stone coping. This concentrated salt residue can lead to etching and premature deterioration of the pool decking and surrounding materials.
Attempting to lower a high salt level is a difficult process that cannot be achieved through chemical treatments. Since salt does not evaporate with the water, the only way to reduce the concentration is by partially draining the pool and refilling it with fresh, unsalted water. This reinforces the importance of maintaining the controlled, manufacturer-recommended salinity range for both equipment longevity and efficient chlorine production.