Hi! Have you ever looked into an ionizer? These units produce copper, silver and zinc ions, and completely eliminate the need for harsh chemicals like chlorine or bromine. With full disclosure in mind, I work for a company that sells them, but we really do believe in them!
The ions add no smell, no color, no taste to the water. Our association with ionizers came about mainly because of our association with wooden hot tubs. Chlorine and bromine in a wooden hot tub can quickly cause unrepairable damage to the wood.
You can see our ionizers at
http://www.almostheaven.net/aho/ionizers.htm. We've had customers who had to abandon their hot tub/spa/pool due to an allergic reaction to other chemical sanitizers. With our ionizer they're once again able to enjoy the water without adverse reaction. Please don't hesitate to reach out to me if you have any questions!