Spa Marvel enzymes must be doing something to affect the bacteria and other waste in the water. We have Spa Marvel in our hot tubs at the cottage and at our home. Not long after using our hot tub at home we headed up to the cottage for almost 2 months. When we returned home the water in our hot tub was still perfectly clear. In the past when we did not have Spa Marvel in the tub, after 2 months at the cottage the water in the tub would be cloudy and smelly. I've tried several different enzyme based products on the market and Spa Marvel has been the best performer for us. We no longer have any cloudy water issues, smelly water, etc...At first we were skeptical so we purchased bacteria test kits to test the water. Even after using the hot tub everyday for an entire week we found no trace of bacteria.
Now from what I understand, Spa Marvel cannot be considered a sanitizer because its not registered and probably does not eliminate bacteria as fast as chlorine or bromine. But it does keep our water clean and as long as its just my family and close friends using the hot tub I am content just having Spa Marvel in it. If my kids have a party and 20 of their friends are using the hot tub, I tend to add some chlorine just make sure.
Since we started using Spa Marvel, we have not had any pH/Alkalinity issues to deal with and we have not had to use any defoamers, descalers, and clarifiers. I would recommend it to anyone who wants to avoid sitting in chemicals.