I've had two residential hot tubs. You really have to stay on top of water quality. Chemical free IMO is BS. I checked water every 4 or 5 days and also drained, scrubbed, changed/cleaned filters. Once the surface (under water) becomes slick or scummy feeling time to treat or change the water. Now for commercial hot tub with who knows what getting in and when or if water checked in community or hotel hot tubs no thanks. I never felt comfortable in hotel hot tub anyway with strangers so close.
