Wizard of water,
Thanks for answering my question (and sry for my bad english writing).
My Caldera spa Kauai has a Ozonator and i use ideed aquafinesse with a despencer with chloor tab.
I have my spa now for 5 months and i keep my wather ok for about 5 months, i use my spa 3 times a week with my wife (2 persons).
My spa has 833 ltr waters and i use every week ca 100 ml aquafinesse and a new chloor tab. My Ph is on this moment is 8.2 little bit to hy, this is with fresh water (2 days old) without aquafinesse, with chloor tab, today 05-07-2015 i put in aquafinesse.