What happens if someone gets into the pool with a skin rash or some other type of infection?
We swim in natural pools all the time, but there's also always the chance for bacterial infection in such a pool, because the water is not sterilized.
The ozone that companies say is useful for reducing the need for chlorine (and these days comes packaged on nearly every spa sold) is actually likely more harmful than the chlorine. It corrodes nearby metal parts, degrades rubber equipment seals and disintegrates vinyl pillows and hot tub covers.
Not a week goes by that we don't hear from a hapless customer who just bought a new spa and has an asthmatic child that can't use it because of the ozone. When ozone levels get high in urban areas, people with respiratory problems are warned to stay indoors and limit their activity.
Metal ionization is great - the best kept secret with regard to pools and hot tubs - but the Nature2 system is just a cartridge that goes in your filter - difficult to adjust the levels. It's telling that they don't even give you a test kit, so that you can measure the ion level.
If you plan to put an ionizer on your pool or hot tub, it should be an electronic device with adjustability and a way to test for proper levels. Also, all ionized tubs and pools should be oxidized weekly to burn up the dead organic matter that accumulates.
Please pardon the plug which seems exceedingly relevant and appropriate in this case...
http://www.almostheaven.net/aho/ionizers.htm 
