Here is what Consumer NZ reported on the SimpleSilver product as recommended by some spa retailers in NZ. Ford HotSpring Spas does not sell this product. Our spas utilise a continuous silver ion purification system in conjunction with C.D. Ozone and a choice of sanitisers which are proven to kill bacteria and viruses in spa pools. Our Freshwater Salt system requires only baking soda and a small amount of salt on spa refill to create just the right amount of chlorine in a gas form which keeps your spa water safe with 1ppm Free Chlorine (which is often the level in town supply; barely detectable). Our Limelight and Highlife models utilise C.D. Ozone which runs 24/7 as does the filtration. Please note that there is no such thing as a chemical/mineral free spa. Minerals/chemicals are required to kill bather introduced bacteria for user safety.
PLEASE READ THIS REPORT HERE https://www.consumer.org.nz/articles/legionnaires-traced-to-spa-pool