There are only three chemicals that will truely sanitize water...chlorine, bromine and peroxide. There are elements that help reduce bacteria such as mineral sticks, ions, enzymes, etc., but they do not kill all organisms that a sanitizer will. This is where Vermonter's input has been valuable. Since testing water is his business, his HotSprings Grandee has been a laboratory from which we all benefit. His routine has come from testing results from his spa. Norhtman has taken Vermonter's routine and elaborated on it from his own experience and engineering background.
Although Nature2 markets its spa routine as almost chorine free, actual testing shows although you might have clear water, there are lots of organisms still lurking in the water (see Vermonter). MPS will not kill anything. What does N2 recommend when your water becomes cloudy, hazy or smelly? Add dichlor. Same goes for Eco One which Vermonter tested with water from Chas spa.
The Frog mineral purifier which is very close to N2 has never tried to sell its product as chorine or bromine free. They always instructed to maintain a reduced sanitizer level (.5-1.0 ppm).
With any one of these systems, you will need to shock your water periodically. This can be acomplished with either chlorine or MPS. The advantage of MPS is that it oxidizes more completely and you can use your spa almost right away. The advantage of chlorine is it supersanitizes your spa.
Bottom line is clear water does not necessarily mean safe water. If you want safe water you need to use one of the three sanitizers. You can REDUCE the amount of sanitizer with one of a number of enzyme or mineral products.
