Your "guy that that works on pools" is just spreading old and bad info that is kept alive by the purveyors of "super non-chemical" (subtitute miracle) water sanitation systems, most of which are dubious at best. It's always "I heard that" or "in another state/country", "the government is about to" etc.

http://www.intox.org/databank/docume...acd/cie286.htm