Coleman uses in the M6 a system with ozone and UVC light that pushes water through a chamber which kills 99.9% of microorganisms, bacteria, viruses and parasites. But I don't mislead people into believing that 99.9% purification is enough to eliminate all sanitizer use in their hot tub. The system dramatically reduces the use of sanitizers, requiring far less PPM. It is my understanding that the EPA will never permit a claim that any system 100% eliminates the use of some kind of sanitizer. An after market system sounds dubious to me. If it worked well then every spa dealer would sell them in their stores........capitalistic dogs that they are.........LOL