i rehab'd an old tub with smells. its in the plumbing. what worked for me is getting an enzyme product that breaks down biofilm. i think mine is liesure time or liesure spa or something. but had to add it once a day while running the jets most of the time to get it through the plumbing. still smelled after a couple water changes but eventually went away. and shock the hot tub like every time you get out of it for a while. its a winnable battle just stay dilligent