Pool salt is the substance used to sanitize water in pools equipped with a salt-water chlorine generator. Understanding the composition of pool salt provides insight into its function and why it is the preferred choice for this unique method of water treatment. The system relies entirely on the salt to create the necessary disinfectant to keep the water clear and safe for swimming.
The Chemical Identity of Pool Salt
Pool salt is chemically identified as Sodium Chloride (NaCl). This compound is structurally the same as common table salt, consisting of a crystalline lattice where sodium ions and chloride ions are bound together. The designation of “pool grade” relates not to a different chemical structure, but rather to an extremely high level of purity, typically 99% or greater.
This high purity is paramount for the effectiveness and longevity of the chlorination system. The salt must readily dissolve in the water to release its constituent ions without leaving behind unwanted residues. Pool-grade Sodium Chloride is specifically chosen because it lacks additives such as iodine or anti-caking agents. These foreign substances can interfere with the electrochemical process within the generator cell and potentially damage the equipment.
Sources and Harvesting Methods
Commercial pool salt is sourced using methods designed to yield the highest possible quality of Sodium Chloride. One common method is solar evaporation, where brine from the ocean or salt lakes is channeled into large, shallow ponds. The sun naturally evaporates the water, leaving behind clean, crystalline salt deposits that are then harvested.
Another significant source is underground deposits mined as rock salt. Solution mining is a third method, which involves injecting water into subterranean salt beds to dissolve the salt. The resulting concentrated brine is pumped to the surface, where the water is evaporated to produce a refined, high-purity product suitable for pool use.
How Salt Generates Chlorine
The purpose of adding salt to pool water is to provide the raw material for the salt-water chlorine generator, which operates through electrolysis. Once the Sodium Chloride dissolves, it dissociates into positively charged sodium ions and negatively charged chloride ions. The water containing these ions is passed through the generator cell, which contains plates coated with rare metals like ruthenium or iridium.
An electrical current is applied across these plates, creating the necessary electrochemical reaction. The negatively charged chloride ions are attracted to the positively charged anode plate, where they form chlorine gas. This chlorine gas dissolves into the water and reacts to produce hypochlorous acid, which is the active sanitation agent responsible for killing bacteria and neutralizing contaminants.
The system is designed to be a continuous, highly efficient cycle. After the hypochlorous acid neutralizes contaminants, it breaks down, and the chloride ions reform. These ions rejoin the sodium ions, effectively reverting back to the original Sodium Chloride compound. This regenerative process means the salt itself is not consumed; only small amounts are lost through splash-out or backwashing, requiring occasional replenishment.
Why Purity Matters: Pool Salt vs. Other Salts
The specific requirements of the salt chlorination system clarify why only high-purity pool salt can be used. Common table salt nearly always contains iodine, which is added for dietary reasons. When introduced into a pool, iodine can cause unsightly yellow staining on the pool’s surfaces due to its reaction with other chemicals.
Table salt and some water softener salts contain anti-caking agents, such as sodium ferrocyanide. These agents can cause the pool water to become cloudy and create residue build-up on the generator plates, reducing the cell’s efficiency. Using road salt or ice melt is even more detrimental, as these often contain high concentrations of insoluble minerals, heavy metals, and dirt. These contaminants can permanently stain pool surfaces or interfere with the electrolysis process, leading to equipment failure.