Saltwater hot tubs

You dissolve a measured dose of salt in the water, and a cell with titanium plates turns it into chlorine. Hot Spring's start-up steps target about 1,750 ppm of salt, and its cartridge is replaced every four months. So a saltwater tub is still a chlorine tub; the difference is that the chlorine is made in the tub instead of poured in.

Hot Spring and Caldera include the system on their top series (Highlife and Utopia) and sell it for their salt-ready series. Master Spas sells its Master Clear system as an option on four series and does not list it for the TS 240X or the Getaway line.

The chemistry, which systems test the water and set their own output, and what salt costs to run are in how salt water hot tub systems work.

The warnings come mostly from brands that don't sell a salt system. Marquis, which sells none, says salt can corrode heaters and exposed metal and that over-chlorination under the cover can bleach pillows and the cover's underside. Bullfrog says it does not offer salt-based systems, and Nordic's owner's manual says a salt system voids its warranty. The makers that do sell one run it at a low salt level, a twentieth of seawater or less, on equipment they warranty; how each system works is in salt water hot tubs.

The rule that follows: use only the salt system the tub's maker sells and warranties, and ask what the replacement cell costs and how often you will buy one. Ozone and UV systems, which most other brands use, are compared on the ozone vs UV page; the rest of the equipment is on the hot tub features page.

• Is the salt system included on this model, or is the tub only salt-ready?
• What does a replacement cell or cartridge cost, and how often will I need one?
• Does the warranty cover the heater and metal parts with salt water?

What a tub costs to run each month, salt or not, is on the hot tub running cost page.