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...It is no longer "theoretical" for spas either since the Dichlor-then-bleach method (or similarly, pure CYA first then bleach ongoing method) has been used and proven in spas since January, 2007 after I first proposed it (waterbear and probably others had mentioned using bleach prior to that, but I first described building up the CYA level some first in January, 2007)... We have also not had the hot tub itch/rash/lung incidents that were being reported previously (from a variety of systems, not just Dichlor-only), but the sample size is way too low to draw conclusions about that...