Non-Chlorine Shock (MPS) Calculator
Non-chlorine shock (potassium monopersulfate, MPS) has no universal dose: use the amount on your bag and scale it to your gallons. At a label dose of 1 lb per 10,000 gallons, a 15,000-gallon pool needs 1.5 lb.
Always follow your product’s label directions. Pool and spa chlorine, bromine, shock and algaecides are EPA-registered pesticides: use products labeled for pool or spa use, and don’t swim or soak until levels are within the limit on your product’s label. If this page and a label disagree, the label wins.
On this page (8 sections)
MPS products differ in strength and in what their labels tell you to do with them, so a dose from one bag is wrong for another. Enter the amount and the gallons from your label, then your pool or hot tub size, and the calculator scales it. The example numbers in the form are placeholders, not a recommended dose. Always follow the product label.
How to scale the dose on your label
Amount for your water = label amount × your gallons ÷ label gallons. A 15,000-gallon pool takes 1.5 times a label dose written per 10,000 gallons. For a hot tub, use the calculator's per-100-gallons line: 0.01 lb (4.5 g) per 100 gallons in the example; multiply it by your tub's size in hundreds of gallons. Weigh small doses on a kitchen scale; a scoop of granules is not a reliable measure.
Some labels list one dose for routine weekly use and a larger one after heavy use. Pick the line that matches your situation and enter it as written. Never go above the largest amount on your label.
What MPS does and does not do
| Question | MPS (non-chlorine shock) | Chlorine shock (liquid chlorine, cal-hypo, dichlor) |
|---|---|---|
| Raises free chlorine | No | Yes |
| Kills germs and algae | No; it is an oxidizer, not a sanitizer | Yes |
| Breaks down sweat, oils, and other swimmer waste | Yes | Yes |
| Effect on pH and alkalinity | May lower both slightly over time | Liquid chlorine and cal-hypo raise pH; trichlor lowers it |
| Adds stabilizer (CYA) or calcium | No | Dichlor adds CYA; cal-hypo adds calcium; liquid chlorine adds neither |
| Effect on the next test | Reads as combined chlorine on DPD tests | Raises free chlorine reading |
| When to use it | Routine oxidizing when the water is clear | Cloudy, green, or slimy water; sanitizer at zero |
The short version: MPS helps chlorine by taking some of the waste load off it, but it can't replace chlorine. If the water is green, cloudy, or slimy, use a chlorine product as its label directs; see how to shock a pool. A technical note from the Pool & Hot Tub Alliance (PHTA) puts it plainly: MPS is not a sanitizer or an algaecide and has to be used together with an EPA-registered sanitizer. The same note says it may lower alkalinity and pH over time, so keep testing both.
Does MPS remove chloramines?
Chloramines (combined chlorine, CC) are chlorine that has already reacted with ammonia and other waste; they cause the "chlorine" smell and red eyes. MPS oxidizes swimmer waste, the material chloramines form from, so routine doses can leave chlorine less to react with. Whether MPS reliably breaks down chloramines that are already in the water, we could not confirm from a primary source. The practical test is simple: if CC stays at 0.5 ppm or more on a test taken before you add MPS, the waste load is more than MPS is handling. You can check CC with the combined chlorine calculator.
Test before you add MPS, not after
MPS left in the water reacts with the DPD reagent used by most chlorine test kits and shows up as combined chlorine. If you test soon after a dose, the kit can report high CC in water that is fine, and you may shock again when you don't need to. Test before you add MPS, or wait until the next day. Some test kit makers sell a reagent that neutralizes MPS before the combined chlorine step; your kit's instructions say whether it has one. How the test separates free and total chlorine is explained in free chlorine vs total chlorine.
Non-chlorine shock in a hot tub
MPS is common in hot tubs because doses are small and it leaves no stabilizer or calcium behind. In a bromine tub, it also turns spent bromide back into active bromine. Scale the label dose to your tub with the per-100-gallons line above. For when to shock and how it fits with chlorine shock in a tub, see hot tub shock; for bromine tubs, hot tub bromine.
When can you swim after MPS?
Follow your product's label. Lanxess, which makes the MPS sold under the Oxone name, describes adding it while the pool or spa is not in use and circulating the water for 15 minutes. Labels differ, though, and some shock products blend MPS with chlorine. Because MPS does not raise chlorine, the chlorine swim limit on your other products is not the issue here; the MPS label is. If you added MPS and a chlorine product on the same day, the chlorine label's limit also applies: test free chlorine before anyone gets in.
Safety
MPS is a strong oxidizer. Never mix it with chlorine, bromine, acid, or any other chemical, dry or in a bucket. Add it to the water, never water to it. Wear gloves and eye protection and don't breathe the dust. Keep the bag closed, dry, and away from heat and other chemicals. Poison Control: 1-800-222-1222. Always follow the product label.
FAQ
Does non-chlorine shock raise chlorine levels?
No. MPS adds no chlorine. It can make a test show more combined chlorine for a while, which is test interference, not extra chlorine.
Is cal hypo a non-chlorine shock?
No. Cal-hypo (calcium hypochlorite) is a chlorine shock: it raises free chlorine and adds calcium. "Non-chlorine shock" means potassium monopersulfate. Check the active ingredient on the label.
Can non-chlorine shock clear a green pool?
No. MPS does not kill algae. A green pool needs chlorine at the level the product's label allows for algae, plus brushing and filtering.
Can you use non-chlorine shock in a salt water pool?
Yes, if the label allows pool use. MPS adds no chlorine and no salt, so it doesn't replace the chlorine your salt cell makes. Test before the dose, not right after.
Sources
- PHTA / AQUA Tech Notes, Potassium monopersulfate (MPS) non-chlorine shock (not a sanitizer; reads as combined chlorine; may lower TA and pH): PDF
- Lanxess, Oxone for pool and spa: lanxess.com
- Taylor Technologies, How FAS-DPD tests for free and combined chlorine values: taylortechnologies.com
- Dose formula: label scaling; see methodology.