Hot tub shock treatment is a weekly oxidiser dose (chlorine or non-chlorine) that breaks down body oils, restores clarity and reactivates your sanitiser.
Hot tub shock treatment is a concentrated dose of oxidiser – chlorine or a non-chlorine alternative such as potassium peroxymonosulfate – that breaks down body oils, sweat, cosmetics and other organic contaminants, restores water clarity and reactivates your existing sanitiser. Shock at least once a week, and again after heavy use, then wait until testing confirms free chlorine is back at 3–5 mg/l (or bromine at 4–6 mg/l) and pH is 7.2–7.6 before bathing.
Your everyday sanitiser kills bacteria, but every soak also adds organic waste – body oils, sweat, deodorant, sun cream – that a normal sanitiser residual works through only slowly. That waste is what makes water dull, foamy or smelly, and it ties up chlorine as chloramines, the compounds behind the classic "chlorine smell" and stinging eyes. A shock dose oxidises that load in one hit: it burns off the organics, breaks chloramines apart and frees your sanitiser to get back to killing bacteria. The result is brighter water, less odour and a sanitiser reading that holds steady instead of vanishing overnight.
Chlorine shock (such as stabilised chlorine granules) both oxidises waste and super-sanitises, so it is the right choice after a water quality problem – green or cloudy water, a suspected contamination, or a tub that has been left uncovered. Non-chlorine shock oxidises the organic load without raising the sanitiser level, produces no chlorine odour, and lets you bathe again sooner – ideal for routine weekly maintenance and essential for bromine tubs, where it also helps regenerate the bromide reserve. Most owners use both: non-chlorine weekly, chlorine when something has gone wrong. Our guide to when to use chlorine vs non-chlorine shock covers the decision in detail.
As a baseline, shock once a week. Add an extra dose when the tub has worked harder than usual:
Busy summer weeks may need two doses; a lightly used winter tub can sometimes stretch the interval – let your test results decide. See how often to shock a UK hot tub for a season-by-season schedule.
Store shock products sealed, cool and dry, and always add product to water – never water to product.
Persistent cloudiness after a proper shock usually points to a tired filter, poor water balance or biofilm in the pipework rather than a lack of oxidiser. Work through cloudy hot tub water causes and solutions before pouring in more chemicals – repeated shock doses cannot fix a mechanical or biofilm problem.
Shock treatment is a concentrated dose of oxidiser added to the water to break down body oils, sweat and other organic contaminants, destroy chloramines and reactivate your everyday sanitiser, keeping the water clear and hygienic.
Shock at least once a week, plus an extra dose after heavy use, after the tub has stood idle, whenever the water looks dull or smells strong, and straight after a fresh fill.
Chlorine shock oxidises waste and super-sanitises at the same time, so it suits problem recovery. Non-chlorine shock oxidises the organic load without raising sanitiser levels, has no chlorine odour and is the routine weekly choice, especially for bromine tubs.
Wait until a test confirms free chlorine has returned to 3-5 mg/l (or bromine 4-6 mg/l) and pH is 7.2-7.6. After non-chlorine shock that is typically 20-30 minutes; after a heavy chlorine shock it can take several hours or overnight.