You should run RO direct as it doesnt like being turned off & on too much
FYI I use a 200L barrel that sits next to my sump a dosing pump on a timer replaces my evap every night with my el cheapo kalk system ie an old powerhead in the barrel
Nobody on this forum is a fish pathologist so why dont one of you send a fish off to the Investigation & Diagnostic Centre,Biosecurity NZ. To see what illness you have for sure??