How Long After Shocking a Pool Is It Safe to Swim?

You’ve just shocked your pool. But it’s super hot and you’d like to swim as soon as possible. When is it safe to swim in your pool after shocking it? How long do you wait?

For chlorine based pool shocks (calcium hypochlorite, bleach and liquid chlorine), it will be safe to swim in 6 hours and up to 5 days after shocking. It’s more important to wait until chlorine levels are below 5 ppm before swimming and the pH is from 7.2 to 7.8, rather than an elapsed time. For Potassium Monopersulfate pool shock, you may wait around 30 minutes.

How long you wait will depend on many factors such as how much shock you used, the type of shock, if it’s an indoor or outdoor pool and the weather.

Let’s explore these further.

woman swimming underwater in a pool
woman swimming underwater in a pool

What Does it Mean to “Shock a Pool”

Shocking a pool means adding up to 2-5 times the normal amount of chlorine  in your pool to raise its chlorine levels within a short period of time. 

It’s also commonly referred to as “superchlorinating” by pool technicians.

I prefer shocking in the evening when the pool is least used and the sun has set. I then leave the pump running till morning by which time and then retest the water.

We have a full article on how to shock your saltwater and chlorine pool:
How to Shock Saltwater Pool | And How Often to Shock It
How To Shock A Swimming Pool For Beginners (In 6 Easy Steps)

Why Should I Shock My Pool?

Some carry out this task as routine maintenance whilst others use it to get rid of algae, to clear a cloudy pool or to increase the amount of free chlorine. Usually you will shock your pool when:

  • There are high levels of organics in the pool (leaves and debris)
  • The pool has algae
  • The pool is cloudy
  • Chlorine levels are extremely low

Why Use High Chlorine Concentration While Shocking Pools?

Using large doses of chlorine (up to 2-5 times the normal amount) is an extremely effective method to break down combined chlorine, organic waste, and other contaminants in the pool.

When there is a large amount of organic matter or algae in the water, it can take a lot of chlorine than usual  to clean up the pool. Once the algae and organic matter are killed by the chlorine, the chlorine levels can be returned to normal.

How Long Do Experts Recommend Waiting to Swim After Shocking a Pool?

Most pool technicians and home owners who regularly shock their pools recommend waiting for at least 24 hours. Sometimes a few days.

Also, as a general rule, the more chemical/chlorine you’ve used in shocking your pool, the more time you’ll need to wait before using it.

Nonetheless, it’s not an exact science. And not every expert can determine the perfect time frame required to wait before using the pool again. Each pool has varying conditions and some factors affect the waiting period.

What’s more important than setting a timeframe, is to wait until the chlorine levels drop to 5 ppm or lower before swimming. That’s when it is safe. This may take a few hours or several days.

You’ll need to test your pool water to know if it’s safe to swim after shocking.

Factors That Determine How Long to Wait To Swim After Shocking

Type of Shock

Cal-Hypo & Sodium Hypochlorite

Most of the time, when we talk about shocking a pool, we mean using sodium hypochlorite or calcium hypochlorite (cal-hypo). Both of these chemicals are chlorine. The former is liquid chlorine and the later is a granular chlorine often marketed as “pool shock”.

Since both of these are chlorines, you will need to wait until the high chlorine levels drop to 5 ppm before swimming. Particularly if you or any of the pool enthusiasts have sensitive skin. Chlorine reacts with proteins and fats on the skin which can cause painful burns.

It’s also important to note that swimming before the this happens, is still risky, even if you don’t feel anything immediately. You may later experience a delayed reaction.

Potassium Monopersulfate Pool Shock

There are also chlorine-free pool shocks on the market. Potassium monopersulfate is one of those.

The advantage of using this product is that you can wait for as little as 15 minutes before jumping into the pool. Potassium monopersulfate is purely oxygen-based and therefore disinfects pools through oxidation. This in turn increases the effectiveness of chlorine present in the pool.

There are however significant downsides to this type of shock which we’ll discuss in another article.

The Amount of Shock Used

A heavier dose usually commands more waiting time before swimming. Although sometimes strong sunlight can help shorten the time required for staying away from your pool.

Algae Content

Pools with higher concentrations of algal blooms require extensive shocking, which can last for several days. The more algae your pool has, the more time it requires for effective disinfection before use.

Pool Maintenance

A pool that’s well-maintained needs less chlorine dosage. This reduces the amount of time needed to stay away from the pool after shocking. The vice versa is true. A pool that’s not regularly maintained will require larger doses of chemicals for it to reach the required standards of pool hygiene.

Manufacturer’s Instruction

I always take advantage of information provided at the back of the package containing the shocking chemical. It helps you know the exact components contained in the shocker and its direction for use.

Every shocker comes with different instructions on how to use it.

Pool Type: Indoor or Outdoor

Outdoor pools will be ready to swim in sooner than indoor pools. The UV rays in sunlight naturally “burns” off the chlorine and reduces the chlorine level. The more sunlight your pool gets, the sooner it will be safe to swim in after shocking.

How to Determine if a Pool is Safe to Swim in After Shocking?

Some common practices people apply to determine the safety of pools include:

  • Visual Inspection – When you can clearly see the bottom of your pool.
  • Free chlorine levels which are determined using testing kits.

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The only accurate way to determine if a pool is safe to swim in after shocking is to test the water. Chlorine levels should be between 1 and 5 ppm and the pH should be 7.2–7.6. If the chlorine is not below 5 ppm, it is not safe to swim in.

Further reading:
Too Much Chlorine in Pool: The Dangers & How to Lower

The pool water should also be clear. If you can’t see the bottom of your pool, you should not be swimming in it. It’s especially a danger for young children as parents and carers may not be able to watch their child at all times.

What Will Happen If I Swim In a Shocked Pool?

I would say the most immediate side effect would be skin irritations. Your swimsuit could start bleaching and losing the strength of its fabric. After all, chlorine is bleach.

If the pool is still cloudy, it may mess up the clarity of your eyesight. This means you won’t clearly see inside the pool, including its bottom and depth, which is a potential safety risk.

The pungent/potent smell of the chlorine/chemical used may be harmful to your lungs and thus pose a major risk on your respiratory system and thus your breathing.

High Chlorine Dangers: What Doctors Say

According to an interview conducted by Health with clinical expert Dr. Gary Goldenberg, MD, assistant clinical professor of dermatology at the Icahn School of Medicine, Mt Sinai, New York City, you’d get dry skin, or perhaps suffer a flare if you have eczema or psoriasis if you swim in a pool with high chlorine levels.

And Jamie Alan, PhD, associate professor of pharmacology and toxicology at Michigan State, mentions other possible symptoms that may come up include burning, pain, blisters, and redness. He also said the effects vary when you’ve inhaled chlorine and if your skin or eye has direct contact.

Other side effects include blurred vision, watery eyes, pain, and redness. If you inhale chlorine, you may experience shortness of breath, wheezing, chest tightness, and fluids in the lungs.

Remedies You Can Take If You Entered a Shocked Pool

Clinical experts, Dr Goldenberg and Alan recommend immediate action once you start noticing symptoms the moment you enter the pool.

First get out of the pool and get some fresh air. Be sure to be some distance away from the pool. Thereafter, remove all clothing and thoroughly wash affected areas with soap and water.

If you still feel uncomfortable on your skin, apply a moisturizer or topical steroid cream if symptoms persist.

If you have breathing problems, call 911 for emergency treatment.

I know how frustrating it is waiting for the pool to be safe enough to swim, but better safe than sorry.

Related Reading:
Do You Need to Shock Hot Tubs?
How to Shock a Hot Tub

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