I copied this from a website that I was reading:
Salt Chlorine Generators, also referred to as Salt Chlorinators, Saltwater Chlorinators or Salt Chlorination Systems, are actually miniaturized chlorine manufacturing plants: the same technology is utilized. The devices are plumbed in-line and work by electrolytically converting salt, in the spa or hot tub water, into chlorine as it passes over specially coated titanium electrode plates. Salt must be added to the water prior to start up, as directed. Thereafter, salt need only be added occasionally, to replace that lost due to splash out, pump outs or backwashing. The device generates Free Chlorine and destroys odorous and irritating chloramines, as the water passes through the cell. Chlorine production is regulated by a controller setting and the equipment operates in conjunction with the timer controlling the filter. Properly used, there is much less sensation of chlorine being present. The other water analysis parameters must be maintained, as with any chlorine-maintained spa or hot tub. It certainly is easy-to-use and convenient and lends itself to automation. Clicking on the underlined and highlighted "keywords" or "catch phrases," in the archived answers will give you access to additional information on that topic or product. Please refer to the Glossary, if there are terms or phrases that require explanation.