What is a non-chlorine shock for swimming pools?

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A non-chlorine shock is a granular treatment used to "shock" your pool or spa that does not contain chlorine or bromine. Instead of killing bacteria directly, its primary job is to act as a powerful oxidizer, breaking down the non-living contaminants that make your water cloudy and smelly.

What Is It Made Of?

The active ingredient in nearly all non-chlorine shocks is potassium peroxymonosulfate (also known as MPS or KMPS). You will often see this listed on the product label along with its chemical formula, 2KHSO₅·KHSO₄·K₂SO₄.

Here are the key properties of this compound:

Appearance: It comes as a free-flowing white granule.

Solubility: It dissolves very rapidly in water.

Key feature: It is a chlorine-free oxidizer, so it will not raise your pool's chlorine or bromine levels.

Why Use Non-Chlorine Shock?

Pool owners choose non-chlorine shock for several practical reasons. You might consider using it if you want to:

Swim Sooner: A major benefit is that you can typically swim just 15 to 30 minutes after adding it, compared to waiting many hours or a full day for chlorine shock to reach safe levels.

Protect Pool Equipment: It does not produce strong chemical fumes that can degrade automatic pool covers or liners, making it a much safer choice for indoor pools or pools with covers.

Improve Chlorine Efficiency: By eliminating organic waste like sweat, oils, and lotions, MPS removes the "dirt" that chlorine normally has to fight, allowing your sanitizer (chlorine or bromine) to focus on killing germs and working more effectively.

Reactivate Bromine: It is very effective at "shocking" a bromine spa to convert spent bromides back into active, sanitizing bromine.

How to Use It

Using non-chlorine shock is a straightforward process. A general guideline is to use about 1 pound (500g) of shock per 10,000 gallons (45,000 L) of water. Be sure to follow the dosage instructions on your specific product's label.

Here are a few tips to get the best results:

Pre-dissolve: While some products allow direct addition, it is often best to pre-dissolve the granules in a bucket of water to ensure they fully dissolve before adding to the pool.

Add at Night: Even though MPS is not broken down by UV light as rapidly as chlorine, it is still a good habit to add any oxidizer at night when the pool is not in use to allow it to work undisturbed.

Check pH: For the best results, ensure your pH is balanced between 7.2 and 7.6 before adding the shock.

Important Safety Note

While MPS is chlorine-free, it is still a strong chemical oxidizer and must be handled with care. As indicated on safety data sheets and product labels, potassium peroxymonosulfate is classified as a hazardous substance:

Corrosive: It causes serious eye damage and skin irritation.

Respiratory Hazard: Inhalation of the dust can cause respiratory irritation.

Environmental Hazard: It is very toxic to aquatic life with long-lasting effects.

Always wear gloves and safety goggles when handling the product and store it in a cool, dry place away from other chemicals.