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All you will get is opinions. There is no data to quantify the benefits of ozone in a spas.I think they work well.
...Can anybody truely say they can tell the difference with one in use as opposed to not having one ?
How does a person know FOR SURE the ozone is working
Ozone is an oxidizer not a sanitizer. Bromine ,Chlorine are sanitizers and oxidizers, but they are not that great at oxidizing. Sanitizing is for bacteria and oxidizing is"shocking". You do not really need an ozonator because you can shock with a sanitizer or a non chlorine shock. A ozonator will reduce the amount of sanitizer you need because a lot of what you add is used up oxidizing not sanitizing. Ozonators are more of an automatic thing and anything you add to your spa to help keep it clean is a good idea.