Why does saltwater pools need chlorine?

The primary reason why saltwater pools need chlorine is for disinfection. Chlorine destroys bacteria, viruses, and other harmful microorganisms that can contaminate the pool water and cause illness.

While the salt chlorinator generates chlorine through electrolysis, the amount may not be entirely sufficient to keep the pool sufficiently sanitised over time, especially in heavy bathing conditions

Oxidation:

Chlorine helps oxidize organic contaminants such as dirt, body oils, and sunscreen lotion that can accumulate in the pool water. Oxidation breaks down these compounds and converts them into harmless substances like carbon dioxide and water, which helps keep the pool water clean and clear.

Algae Control:

Chlorine also effectively prevents and controls algae growth in swimming pools. Algae require nutrients, sunlight, and moisture to grow, they thrive on the same organic contaminants that chlorine targets through oxidation making a chlorinated pool less favorable environment for such growth. With adequate residual chlorine , you will experience little to no algae problems in your saltwater pool. Maintaining a free chlorine level of at least 2mg/L will give pool owners a "peace of mind".