How to shock a hot tub
In brief
Shocking is a strong oxidizer dose that burns off the body oils, sweat, and contaminants a normal sanitizer level leaves behind. Balance pH to 7.2 to 7.8 first, size the dose for your gallons, add it with the pump running and the cover off, and wait before soaking: until chlorine falls back near 5 ppm for a chlorine shock, or about 15 minutes for a non-chlorine (MPS) shock.
Sanitizer keeps the water safe moment to moment, but it gets used up fighting the load every soak adds. A weekly shock resets that, which is why regularly shocked water stays clear and shock-skipped water turns cloudy and starts to smell.
How to do it
- Test and balance pH. Shock works best with pH in 7.2 to 7.8. Correct it first if it is off.
- Size the dose. Use the dosing calculator for your gallons rather than guessing; too little does nothing, too much just makes you wait longer.
- Add it correctly. With the pump running and the cover open, broadcast the shock across the water. Leave the cover off afterward so the gas vents instead of attacking the cover underside.
- Wait, then retest. For chlorine shock, wait until the level falls back near 5 ppm before soaking. For MPS, about 15 minutes is typical, but follow the label. Retest to confirm.
Go in small steps with the water moving, pause, retest, then decide on more. Never mix one chemical with another; the label on the container beats any guide, including this one.
Chlorine shock or non-chlorine (MPS)?
Chlorine shock (dichlor) both oxidizes and sanitizes, so it doubles as a sanitizer boost, but it raises your chlorine sharply and you wait for it to come back down before soaking. Non-chlorine shock (potassium monopersulfate, or MPS) oxidizes without raising chlorine, so it has a short wait and suits a quick weekly refresh and bromine tubs (it also helps reactivate spent bromine). A common split: MPS for the routine weekly shock, chlorine for after heavy use or to clear a problem.
What helps
A dichlor chlorine shock for sanitizing power, or a non-chlorine MPS shock for a quick weekly refresh and bromine tubs.
The source for these figures
Every dose on this page is computed from the standard published rates in these references, and the build re-checks each constant against them before the site ships (how the checking works).
- Taylor Technologies dosage tables · the standard pool and spa water-chemistry dosage reference the dosing constants are calibrated against
- PoolMath (Trouble Free Pool) · the public pool and spa dosing calculator the constants are cross-checked with
- Pool & Hot Tub Alliance (PHTA) · the industry association whose balanced-water guidance sets the target ranges
Asked often
How long after shocking can I get in?
For a chlorine shock, wait until the chlorine level falls back to about 5 ppm or lower, which can be 20 minutes to a few hours depending on the dose; test before getting in. For a non-chlorine MPS shock, about 15 minutes is typical. Always follow the wait time on your product label.
How often should I shock my hot tub?
Weekly is a good baseline for regular use, plus an extra shock after a party or heavy soak. If the water smells or looks dull, shock it. Shocking is the routine reset that keeps sanitizer working and water clear.
Why did the water go cloudy after I shocked it?
A brief haze right after a large dose is normal as the oxidizer works and disperses. Keep the pump running and it usually clears within a few hours. If it lingers, check the filter and your balance, covered in the cloudy water guide.