Shock weekly, plus after every heavy session. Here is why both are needed, and how to scale the routine to a tub used twice a week vs daily.
The simple answer is once a week, plus immediately after any session with three or more bathers. The reason for both is that shock does two different jobs: it knocks down the chloramines that build up over time, and it deals with the spike of organics from a busy session.
Pick a day, ideally an evening when the tub is unused. Add a normal dose of non-chlorine shock per the bottle. Run the jets for 15 minutes with the cover off. Cover and walk away.
By morning, combined chlorine should be below 0.5 ppm and the water should be at its sparkling best.
For a tub used only at weekends, shock on Sunday evening so the water is fresh by the next Saturday.
After any session with three or more bathers, dose half the weekly amount of non-chlorine shock as soon as the last person is out.
Leave the cover off for an hour with the jets running on slow. The cover-off period lets the chloramines vent.
This routine prevents the slow accumulation of chloramines that creates the harsh-smelling water owners often associate with shock being needed every other day.
Daily-use tubs (gym, hotel, busy family): shock at the end of every day with the maximum bottle dose.
Lightly used tubs (once a week): the standard weekly shock is plenty.
If you are noticing combined chlorine creeping up between shocks, the dose is too small for the load. Increase the dose, not the frequency.
Yes. Once the water is up to temperature and you have set the initial sanitiser and pH, a small chlorine shock kicks the system off cleanly.
With non-chlorine shock, essentially no. With chlorine shock, yes. Overdosing chlorine bleaches headrests, irritates skin, and wastes product. Stick to the bottle.