If you want to use an EPA-approved disinfectant that is not halogen-based (i.e. not chlorine or bromine), then there are two choices: Nature2 with MPS (and occasional Dichlor) or Baquacil/biguanide/PHMB. Nothing else (other than chlorine or bromine) will kill bacteria quickly enough to pass
EPA DIS/TSS-12 which is what is required to be called a disinfectant for pools or spas and to make claims of killing bacteria.
Metal ions alone do not kill quickly and copper ions at pool/spa concentrations do not even control bacterial growth for the fecal bacteria
Escherichia coli,
Staphylococcus aureus and
Enterococcus faecium (and probably
Enterococcus faecalis as well). These bacteria live in the G.I. tract and have resistance to low levels of copper ions since blood serum normally has 0.8 to 1.1 ppm copper ions (details about metal ion systems are in
this post). Enzyme products may help break up biofilms, but it is not clear how quickly they kill bacteria and whether they kill faster than bacteria can reproduce.
In practice, the risk of illness is low in residential pools and spas because, unlike commercial/public pools and spas, you don't have the situation where one person can infect dozens if not hundreds or more (in pools). Nevertheless, don't fool yourself into thinking that these alternative systems are as sanitary as using an EPA-approved disinfectant. It's a spectrum of risk, but the risk with the EPA-approved disinfectants is far lower.
Richard
