What Is Non-Chlorine Shock? (And Should You Use It In A Pool?)


by Rick Patterson

Shocking a pool is a fairly regular occurrence when it comes to pool maintenance.

In most cases, pool shocking requires the use of chlorinated shock. But, gaining in popularity in the past decade, is the practice of using non-chlorine shock. It certainly has its place and can help keep the pool clean over time. 

The big question is should you, or do you even need to use it?

What Is Non-Chlorine Pool Shock?

To understand what non-chlorine pool shock does, it’s important to first understand what pool shock is and why it’s used in the first place.

Traditionally, shocking a pool refers to dosing the pool’s water with a large amount of chlorine.

What does this achieve? Well, chlorine is both a sanitizer and an oxidizer, and it keeps the water sparkling clean.

When microorganisms, bacteria and organic matter are present in pool water, chlorine goes to work, keeping the pool safe to swim in. When chlorine levels in the pool get low, chlorinated pool shock treatment is added to restore the balance.

On the flipside, we have non-chlorine pool shock (aka potassium monopersulfate, or MPS), which is actually an oxidizer that comes in 1lb. bags of granular powder (just like chlorinated shock). This is an ideal shock alternative for chlorine free pools that aren’t using chlorine as their sanitizer. 

Why Use Non-Chlorine Shock?

So let’s break this down further to clarify when to use chlorine vs non-chlorine shock.

Chlorine becomes less effective as it cleans, and sunlight also destroys it. Therefore, after a certain amount of time, it needs to be topped up. If its level dips too low, there won’t be enough of it to keep the pool sanitized.

It’s at this point where pool water chemistry becomes troublesome, with chloramine, algae blooms, and other unsanitary conditions taking over.

This is when you’ll use chlorinated shock to eradicate every single living organism in the water and simultaneously top up the chlorine level at the same time.

So, if chlorine is imperative to killing nasties in the water, and making it healthy again, why would you ever use a shock that doesn’t contain chlorine?

Lightens The Load On Free Chlorine

Remember, chlorine is a 2-in-1 sanitizer and oxidizer. Non-chlorine shock is only an oxidizer, and only destroys oils and organic matter in the water.

It allows for the free chlorine (that’s already present in the pool water) to be more efficient at disinfecting the pool. The non-chlorine shock will take care of oxidizing the water, essentially taking half of chlorine’s job off its plate. 

The free chlorine now has a lighter load and can focus solely on only sanitizing the water. It will also stay effective longer as it’s no longer doing both the sanitizing and oxidizing of the pool water pollutants.

Suitable For All Pool Types

Non-chlorine shock treatment is suitable for all types of pools, whether they’re inground, semi inground, or above ground. It’s also pool finish friendly, unlike chlorine which can fade and damage vinyl liners.

Additionally, non-chlorine shock is ideal for more gentle pools that use a saltwater system.

Won’t Increase Chlorine Levels

Because MPS shock is an oxidizing agent that doesn’t contain chlorine, the existing level of chlorine in your pool water will remain constant.

Similarly, if you’re using bromine, you can use MPS shock and the bromine levels won’t be affected. This lack of chlorine also means it won’t produce any combined chlorine (aka chloramines) when added to the water.

Won’t Increase Cyanuric Acid Levels

Cyanuric acid (aka CYA, aka pool stabilizer) is a sunlight protectant for chlorine. Without CYA in the water, chlorine will be eaten up by the sun’s UV rays within a matter of hours. Non-chlorine shock doesn’t contain CYA, therefore the CYA levels in the pool won’t rise when you use it. 

Why is this important? 

Too much CYA in the pool can “lock” the pool’s free chlorine. If this occurs, the residual chlorine becomes less effective as a sanitizing agent, and water issues will arise.

Won’t Increase Calcium Levels

One of the most popular chlorinated shocks is calcium hypochlorite, which contains, you guessed it – calcium! 

While the chlorine in this shock will eventually die off, the calcium it contains stays present in the pool water. This is fine if your pool has low calcium levels, but terrible if the levels are already ideal. This will lead to high calcium levels in the pool water which is commonly known as calcium hardness, or scale.

By using a non-chlorinated shock (which doesn’t contain any calcium), potential hard water and scale issues can be avoided.

Great For Spas/Hot Tubs

Non-chlorine pool shock is also very stable in high water temperatures. This makes it ideal for use in spas or hot tubs, where the spa water temperature can reach up to 102°F.

Restores Water Clarity

Non-chlorine shock does an excellent job of restoring the clarity of pool water by oxidizing the organic pollutants that are in it. This leaves your pool looking its best with a minimal amount of effort.

Can Shock At Any Time

Unlike chlorinated shock, you can use MPS shock at any time of day because it won’t be burned up by the sun. It also provides a quick turnaround time, and you can be back in your pool 15 mins after shocking with MPS.

When Shouldn’t You Use It?

There are a few drawbacks when it comes to non-chlorinated shock, with the first being that it won’t kill off bacteria or algae. Only chlorinated shock can tackle those bad boys.

Secondly, MPS shock has a very acidic pH level of 2.3. If too much is added, it can cause the overall pH level of the pool to drop for a sustained period, which you’ll then have to raise. Whereas, with a chlorinated shock, if you overdose the pool on it, all you have to do is wait a few extra hours for the sun to burn off the chlorine.

Finally, using a non-chlorine shock treatment will lower the pool’s total alkalinity, and at the same time, raise the TDS (total dissolved solids) level in the water.

How Do You Use Non-Chlorine Shock?

The step-by-step process for using non-chlorine shock is much the same as traditional, chlorinated shock. 

  1. Suit up! While MPS shock is much gentler than chlorine, you should still wear the proper safety equipment, such as protective eyewear, gloves, and clothing when working with any pool chemicals.
  1. Measure out how much shock your pool requires. A single bag of shock is usually 1 lb. per 10,000 gallons of water. This makes the math easy, but always consult the instructions to get the correct dosage for the shock you’re using.
  1. Non-chlorine shock is fast dissolving and less harsh than its chlorinated counterpart, with some people literally pouring the bag of shock directly into the pool. We recommend making a shock solution. Do this by filling a 5-gallon bucket with water, adding in the powdered shock, and mixing it using a wooden stir-stick.
  1. Walking around the perimeter of the pool, slowly pour the shock solution into the water. This makes it easy for the return jets to circulate it throughout. 
  1. Wait 15 minutes. Once the timer goes off, jump in the pool!

Pool Shock, Hold The Chlorine.

Non-chlorine shock isn’t really “shock”, but more just an oxidizing agent for your pool.

It doesn’t function the same as a traditional chlorinated shock does, so you have to be aware of how it interacts with your pool before deciding if it’s the best solution to keeping your pool water clean over the long haul.

Categories: Pool Care, Pool Chemistry