How to Shock a Hot Tub
Shocking a hot tub clears combined chlorine, odors, and organic buildup. Here's when to shock, which shock to use, how much you actually need, and how long to wait.
Updated July 2026
Quick answer
Shock a hot tub by balancing pH first, then adding enough chlorine shock (dichlor) or non-chlorine shock (MPS) to bring free chlorine to roughly 10–15 ppm, with the jets running and the cover off. Shock weekly, after heavy use, or whenever the water smells of chlorine — then wait until free chlorine falls back to 3–5 ppm before soaking.
When to shock
- On a regular schedule — about once a week for typical use.
- After a party or heavy soak that added a lot of bather load.
- When the water smells strongly of chlorine — that odor is combined chlorine (chloramines), a sign you need to shock, not that you have too much.
- When water looks dull or cloudy despite an okay sanitizer reading.
Chlorine shock vs. non-chlorine shock
Chlorine shock (dichlor) both sanitizes and oxidizes — it kills and clears in one step, but raises your chlorine level, so you wait longer before soaking. Non-chlorine shock (MPS, potassium peroxymonosulfate) oxidizes away organics and odors without adding chlorine, so the water is usually swimmable much sooner. Many people alternate: chlorine shock to sanitize, MPS for a quick refresh.
How much shock do you need?
Aim at a number, not a scoop. A shock should bring free chlorine to roughly 10–15 ppm — high enough to break chloramines apart, then fall back on its own. That target is the answer; the amount of product is just how you reach it.
Which is why no universal "add two capfuls" rule works. Two things set the amount:
- Your volume in gallons. Twice the water needs roughly twice the product — and most people are unsure of their tub's real volume, which is where the guessing starts.
- The product's concentration. Dichlor is commonly sold at 56% or 62% available chlorine, and non-chlorine shock strengths vary too. The same spoonful from two different tubs of shock does not do the same thing.
So dose to the target rather than to habit: your label states how much of that product raises a given volume, so measure it against your gallons instead of eyeballing a scoop. After a heavy soak or with cloudy water you are aiming at the top of the 10–15 ppm range, not the bottom.
Aquavail does that arithmetic for you — your tub's volume, your sanitizer, your current reading — and then tells you when free chlorine has dropped back to a safe soaking range.
How to shock, step by step
- 1
Test and balance pH
Shock works best with pH in the 7.2–7.8 range. Adjust before you add it.
- 2
Remove the cover and run the jets
Circulation disperses the shock and lets gases escape. Never shock with the cover closed.
- 3
Dose to the target, not to habit
Aim to bring free chlorine to about 10–15 ppm. Check your label for how much of your product raises your tub's volume — concentrations differ — and measure it rather than eyeballing.
- 4
Add shock to the water
Pour the measured shock into the moving water, following the product label.
- 5
Keep circulating with the cover off
Give it time to work and off-gas — typically at least 15–20 minutes, longer for a full chlorine shock.
- 6
Re-test before you soak
Wait until free chlorine falls back to roughly 3–5 ppm before getting in.
Aquavail calculates the shock dose for your tub and sanitizer, and tells you how long to wait — so you're not guessing whether it's safe to get back in.
Common questions
How long after shocking a hot tub can you use it?
After a non-chlorine (MPS) shock, often around 15–20 minutes of circulation. After a chlorine shock, wait until free chlorine drops back to the 3–5 ppm range — that can take a few hours. Always re-test rather than going by the clock alone.
Why does my hot tub smell like chlorine after I shock it?
A strong chlorine smell is chloramines — chlorine that's already combined with contaminants — not excess fresh chlorine. It usually means you needed to shock. A proper shock breaks those chloramines apart, and the smell fades as the water clears.
How much shock does a 400-gallon hot tub need?
There's no single answer, because the product matters as much as the tub. Aim at the outcome instead: enough shock to bring free chlorine to roughly 10–15 ppm. A 56% dichlor and a 62% dichlor need different amounts to get a 400-gallon tub to the same place, so read the label for your product, measure against your actual gallons, and re-test — rather than trusting a remembered scoop count.
Can you over-shock a hot tub?
You can add more than needed, which just means waiting longer before it's safe to soak and putting extra wear on the water. Dose to the 10–15 ppm target using your product's label and your tub's volume rather than eyeballing it, and let the level come back to 3–5 ppm before use.
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