Saltwater pool
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Saltwater pools use dissolved salt (3,000-6,000 ppm) as a store for the chlorination system. The chlorinator uses electrolysis to break down the salt (NaCl) and release the chlorine into the water. The main advantage of this is that the main chemical added to the pool is salt which is harmless compared to the usual bleaching agents like chlorine. As such, a saltwater pool is not actually chlorine-free; it simply utilizes a chlorine generator instead of direct addition of chlorine. When chlorine levels are low in the pool, your salinity level is down, you increase chlorine levels by adding more salt into the pool. Salt count can be lowered due to splash out, backwashing, and evaporation.
[edit] Technique
To super chlorinate the pool, as is recommended monthly, the chlorinator and pump are left to run for 24 hours rather than the usual 8. Note that super chlorination is not a substitute for oxidation. It is recommended to shock/oxidize your pool weekly to break down bacteria and contaminants that may get in your pool as well as to help prevent algae. Super chlorination is not strong enough to oxidize a salt water pool.
The chlorinator cell consists of parallel plates made of a mesh coated with ruthenium, iridium and titanium. The cell needs regular cleaning in a mild acid solution (1 part HCl to 15 parts pool water) to remove the buildup of calcium which can reduce the effectiveness of the cell. Running the chlorinator for long periods with not enough salt in the pool can strip the coating off the cell which then requires an expensive replacement as can using too strong an acid wash.
Saltwater pools also require stabilizer (cyanuric acid) to help stop the chlorine from evaporating out of the pool. Usual levels are 60-80ppm. They also require the pH to be kept between 7.0 and 7.8 with the chlorine being more effective if the pH is kept closer to 7.0. The salt levels are much less than the ocean, which has salt levels of around 35 parts per thousand (ppt)[1]. The salt is poured across the bottom of the pool and swept with the pool brush until it dissolves. Concentrated salt solution should not be allowed into the skimmer as it may damage the cell or controller.
