Salt-water chlorinators electrolyse low-salt water into chlorine on demand. They are quieter than dosing by hand, but they are not chemical-free.
Yes, salt-water hot tubs are a real category. They use a low salt level (typically 1,500 to 2,500 ppm, much less than seawater) and a small electrolytic cell that converts salt to chlorine on demand. The water feels softer, the smell is reduced, but you still need to test, balance, and shock just like a conventional setup.
Generates chlorine from salt as needed, removing the daily or weekly hand dosing.
Produces a low, steady residual rather than the peaks and troughs of granular dosing.
The water feels noticeably softer and the smell is reduced because chloramines build up more slowly under steady chlorination.
It does not replace the need to balance pH, alkalinity, and calcium. The chemistry rules are the same as for any chlorinated tub.
It does not eliminate shocking. You still need a non-chlorine oxidiser weekly to deal with chloramines and organic build-up.
It does not work well with low-quality fill water. Iron in the supply will stain the cell. Hard water will scale it. A pre-filter on the refill hose is more important here than for a conventional tub, not less.
Initial cost: 600 to 1,200 pounds for a retrofit kit, more for a built-in system on a new tub.
Cell life: typically 2 to 4 years for a hot tub cell, depending on usage. Replacement cells are 200 to 400 pounds.
Salt and electricity to run it: a few pounds a month, much cheaper than buying chlorine in granular form. The maths usually works out at break-even after about 18 months for a heavily used tub.
Modern salt-compatible heater elements are designed for this. Older tubs with copper components should not be retrofitted without checking the manufacturer's compatibility list.
No. The salt level is far too low to taste or smell. Most bathers cannot tell salt water from regular hot tub water by skin feel alone.