There are products like Baqua Spa, which is not chlorine or bromine based, and that regimen is pretty darn spendy. We couldn't get it to work, and abandoned it after about a year.
I've heard that ozone reduces the need for certain chemicals, but I don't have ozone so I don't know the reality of it. But then again, I've heard possible bad things about ozone and health, too.
Talk to a couple spa dealers in your area and see what they offer, and how much more it costs than the basic dichlor or bromine.
8 million spas! Wow way more than I thought.