You could use chlorine after you exit the spa in doses that allow it to dissapate before your next use, down to .5-0 PPM. Then a mineral purifier and ozonater between uses to help maintain clean water. Then your not soaking in "chemicals" as they say because there is a super low reading of chlorine during your soak, more like drinking water, and a higher more effective at killing bacterial level after. THis works for alot of people.