How to shock a hot tub
Quick answer
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.
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). Many owners use MPS for routine weekly shocks and a chlorine shock after heavy use or to clear a problem.
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.
Add in small steps with the pump running, wait, then retest before adding more. Never mix chemicals together, and always follow your product label, which wins over any calculator.
What helps
A dichlor chlorine shock for sanitizing power, or a non-chlorine MPS shock for a quick weekly refresh and bromine tubs.
Get spa chlorine shock Get non-chlorine shock (mps)
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Common questions
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.