Hot tub shock
Hot tub shock is a large oxidizer dose that burns away sweat, oils, and used-up chlorine. Non-chlorine shock takes 0.8 oz (23 g), while chlorine shock takes 0.2 oz (5.7 g), for each 100 gallons (380 litres). Shock the water about once a week and also after heavy use.
To see how much to add, choose the shock you own and your tub.
- Chlorine shock (dichlor) for 100 gal of water
- 0.2 oz (5.7 g)
- Chlorine-free shock (MPS) dose for each 100 gallons
- 0.8 oz (23 g)
- Also apply after heavy use
- Weekly
- Keep the lid open once shocking is done
- 20 min
Comparing chlorine shock with non-chlorine shock
| Non-chlorine shock (MPS) | Chlorine shock (dichlor) | |
|---|---|---|
| Active chemical | Potassium monopersulfate | Sodium dichlor, 56% available chlorine |
| Dose per 100 gal (380 L) | 0.8 oz (23 g) | 0.2 oz (5.7 g) |
| Raises chlorine | No | Yes |
| Adds cyanuric acid | No | Yes, it builds up with repeat use |
| Works with | Chlorine, bromine, mineral or ozone tubs | Chlorine tubs |
| Best for | This works for weekly upkeep while sanitizer is in range and for waking up a bromide bank. | Low sanitizer, cloudy or smelly water, heavy use |
| Wait to soak | About 15 minutes, if the label agrees | Until free chlorine is back to 5 ppm (parts per million) or under |
Data here come from Leslie's plus the EPA dichlor label. MPS acts as an oxidizer rather than a sanitizer, meaning it cannot correct low chlorine alone.
By weight, dichlor is far stronger. According to the Hot Spring manual, 1 teaspoon of it equals about 2 tablespoons of MPS in effect. Hot Spring, a hot tub manufacturer, recommends 3 tablespoons of MPS per 250 gallons for weekly non-chlorine shocking.
Hot tub shock calculator: dose for your gallons
| Tub size | Chlorine shock (dichlor) | Non-chlorine shock (MPS) |
|---|---|---|
| 180 gal (680 L) | 0.4 oz (10 g) | 1.4 oz (41 g) |
| 250 gal (950 L) | 0.5 oz (14 g) | 2 oz (57 g) |
| 290 gal (1,100 L) | 0.6 oz (16 g) | 2.3 oz (66 g) |
| 350 gal (1,320 L) | 0.7 oz (20 g) | 2.8 oz (79 g) |
| 500 gal (1,890 L) | 1 oz (28 g) | 4 oz (113 g) |
The EPA label guides Dichlor use: 1 oz per 500 gallons. The Leisure Time Renew label guides MPS use: 2 oz per 250 gallons. Always follow your specific product label if it differs. Leslie's notes that adding more shock is not always better.
Not sure what size you have? First, check how many gallons your hot tub holds.
What are the chlorine and shock amounts for hot tubs holding 200, 250, 300, 350, 400, or 500 gallons?
| Tub size | Chlorine granules to raise free chlorine 1 ppm | Chlorine shock (dichlor) | Non-chlorine shock (MPS) |
|---|---|---|---|
| 200 gal (760 L) | 0.05 oz (1.4 g) | 0.4 oz (11 g) | 1.6 oz (45 g) |
| 250 gal (950 L) | 0.06 oz (1.7 g) | 0.5 oz (14 g) | 2 oz (57 g) |
| 300 gal (1,140 L) | 0.07 oz (2.0 g) | 0.6 oz (17 g) | 2.4 oz (68 g) |
| 350 gal (1,320 L) | 0.08 oz (2.4 g) | 0.7 oz (20 g) | 2.8 oz (79 g) |
| 400 gal (1,510 L) | 0.10 oz (2.7 g) | 0.8 oz (23 g) | 3.2 oz (91 g) |
| 500 gal (1,890 L) | 0.12 oz (3.4 g) | 1 oz (28 g) | 4 oz (113 g) |
Locate your tub size, then look across the row. For everyday top-ups, use the chlorine column for your chlorine granules. Those granules are sodium dichlor, with 56% available chlorine per the EPA label. Put your strip reading into the chlorine level calculator and it figures the dose. Use the shock calculator above for any other sizes.
How often should you shock?
About once a week is the schedule Leslie's suggests, plus a shock after heavy use. Increase frequency when multiple people soak, sanitizer levels fall quickly, or water turns cloudy or smelly.
The ideal time is immediately after soaking so the shock can work before anyone returns. You should also shock when total chlorine readings exceed free chlorine levels. This method commonly fixes cloudy water and foam too.
Steps for shocking a hot tub
- Start by testing. Check every pad using test strips. Before shocking, Leslie's recommends keeping pH between 7.2 and 7.8.
- Switch on the jets. Moving water spreads the shock around.
- Measure out the precise amount. Use a dry, clean scoop reserved just for this item.
- Scatter it over the surface. The EPA dichlor label says to add it straight to the tub and never pre-mixed. Do this when it is not windy.
- Keep the lid off. At least 20 minutes is what Hot Spring asks for so gas can escape. Vinyl under the cover can discolor if gas gets trapped.
- Test the water before entering. Enter only after sanitizer levels return to normal.
Time to wait before soaking
With MPS, the Leisure Time Renew label allows a soak again after about 15 minutes. Chlorine-free shock often shortens the wait, and Leslie's agrees. MPS may cause some chlorine tests to show high results, so test again if a reading seems strange.
Following chlorine shock, wait until free chlorine drops to 5 ppm or less per the EPA label. Lay-Z-Spa tells owners to wait at least 24 hours after dosing with shock.
You must never mix two shocks, and do not shock with any other chemical either. Dichlor can release toxic gas if it touches even a little water, so keep lids shut and scoops dry.
Common questions
Is non-chlorine shock okay to use in a chlorine hot tub?
Yes, you can. Chlorine, bromine, mineral and ozone systems work with MPS where the manufacturer allows it, according to Leslie's. If the pad reads under 3 ppm, add chlorine too because this product won't raise low levels.
When can you enter a hot tub following a shock treatment?
If the label agrees, wait about 15 minutes after using non-chlorine shock. Stay out until free chlorine hits 5 ppm or less after using chlorine shock.
Is it a good idea to shock my hot tub after every use?
This applies only if there is heavy use. Leslie's recommends roughly weekly treatments plus after busy soaks, with right after soaking being ideal.
Can you add too much shock to a hot tub?
Yes, you can. Follow the label amount exactly since adding more does not help. Free chlorine stays above the 5 ppm soak limit longer if you use too much chlorine shock.