By The Zagosa Team. Published .
Reviewed or updated .
The short answer: once a week, plus straight after any session with three or more bathers. You need both because shock covers two separate jobs. It knocks down the chloramines that gather over time, and it deals with the surge of organics from a busy soak.
The weekly upkeep shock
Choose a day, ideally an evening when the tub is idle. Add a normal dose of non-chlorine shock as the bottle directs. Run the jets for 15 minutes with the cover off, then cover up and leave it.
By morning, combined chlorine should be below 0.5 ppm and the water at its sparkling best.
For a weekend-only tub, shock on Sunday evening so the water is fresh again by the following Saturday.
The after-session top-up
After any session with three or more bathers, dose half the weekly amount of non-chlorine shock the moment the last person is out.
Leave the cover off for an hour with the jets on slow. That cover-off spell lets the chloramines vent away.
This habit heads off the slow chloramine build-up that leaves the harsh-smelling water owners so often blame on needing to shock every other day.
When to scale the routine up
Daily-use tubs (gym, hotel, busy family): shock at the end of every day at the maximum bottle dose.
Lightly used tubs (once a week): the standard weekly shock is plenty.
If combined chlorine keeps creeping up between shocks, the dose is too small for the load. Raise the dose, not the frequency.
Common questions
Should I shock a brand-new tub before first use?
Yes. Once the water is up to temperature and you have set the initial sanitiser and pH, a small chlorine shock gets the system off to a clean start.
Can I overshock?
With non-chlorine shock, essentially no. With chlorine shock, yes. Overdosing chlorine bleaches headrests, irritates skin, and wastes product. Stick to the bottle.