How Long Do You Have to Wait to Swim After Shocking a Pool?

  • By: John Parker
  • Last Updated: October 7, 2022

Shocking a pool is part of the regular pool maintenance that pool owners need to carry out to keep the pool water quality in good condition. It is important to know how long after you shock a pool can you swim and be safe.

For this reason, I normally shock my pool in the evening and then leave the pool pump running overnight. That way the swimming pool water is normally safe to swim in by the next morning.

Read on for a full description of how long should you wait to swim after putting shock in the pool.

how long to wait after shocking pool
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How long after shocking pool can you swim

It is very easy for pool owners to give in to pressure from children and others, who are desperate to get in the swimming pool and swim, and not wait long enough after shocking a pool for the level of chlorine in your pool water to reach a safe level. But stand firm!

When it comes to how long does shock take to work, the accepted rules of thumb in the swimming pool industry for how long after you shock a pool can you swim are:

Wait 24 hours

Many say that once you use pool shock, no-one should swim for 24 hours. Certainly, if you do wait this long then it is almost definitely going to be safe for people to swim by then.

But many people don’t want to wait this long and, to be honest, in my experience, it is not normally necessary.

However, you shouldn’t just assume that if you leave it overnight that it is then safe for swimming. You should check the level of chlorine first, as below.

Test free chlorine levels

This is the method I use.

After shocking a pool I wait for at least a few hours – actually, since I normally shock my pool in the evening, and then run the pump overnight, it is normally more than eight hours anyway, often more like 12 hours since I am certainly not an early riser.

I then test the pool water using a test strip to check the level of free chlorine.

Provided these are at 5ppm or less then the pool is safe to swim in. If they are higher then I leave it another hour or so before testing again but, to be honest, it is quite rare that the levels haven’t dropped below these levels overnight.

When to shock a pool

There are a number of different reasons and events that will make it necessary for a pool owner to shock a pool. Shock your pool when:

  • Start up or opening
    When you first start up the pool or open it at the beginning of the season.
  • After heavy rain
    Rain can bring with it contaminants and perhaps also lower the pH level (as rain is often quite acidic).
  • Heavy use
    After the pool has received heavy use, perhaps after a children’s pool party or some similar event.
  • Free Chlorine level low
    If you test your pool water and the free chlorine level is zero or just above then shocking is a good idea to increase the free chlorine levels.
  • Algal Blooms
    If there is a sudden Algae bloom then you will need to shock your pool by super-chlorinating (using up to 4 times the normal dosage)
  • Water temperature
    If the temperature of the pool water increases due to a spell of very hot weather this can increase the growth rate of bacteria.
  • After an “accident”
    Perhaps you have had a young child in the pool whose swim diaper didn’t do as good a job as it should have done.
  • End of season
    Shocking when you close your pool in winter can make life easier when you reopen it in spring.

Types of pool shock

how long after shock can you swim - Chlorine or Oxygenizer

Different types of pool shock can make a difference to how long after shocking you can swim so the first piece of advice would be to read the manufacturer’s instructions on the packaging. This should tell you how long after shocking your pool to wait using that particular type of pool shock.

Chlorine shocks

There are two main types of chlorine pool shock (that is, shock containing Chlorine) which are Calcium Hypochlorite (often referred to as Cal-Hypo) and Dichloroisocyanuric acid (often referred to as Di-Chlor).

Cal-Hypo is the one you will see for sale most often, primarily I guess because it is not only the cheapest but strong too. It is very quick to dissolve (always in a bucket or container pre-filled with water before being added to the pool).

A very popular Cal-Hypo pool shock available on Amazon is the In The Swim Chlorine Pool Shock which comes in 24 x 1 pound bags.

Di-Chlor is a granular chlorine that includes a stabilizer. It is slower dissolving than Cal-Hypo and the stabilizer will raise the cyanuric acid level in your pool. In the Swim Sodium Di-Chlor Chlorine Shock is available in 24 1-pound bags on Amazon.

ALWAYS READ THE INSTRUCTIONS AND PRECAUTION WARNINGS ON THE PACKAGING!

Liquid chlorine shock

You can also buy a liquid chlorine shock which doesn’t require pre-mixing or dissolving before pool shocking. Adding liquid chlorine can be more expensive but it is a very easy way of shocking your pool but won’t make any difference to how long after shocking you have to wait before you can swim.

A popular liquid chlorine shock available on Amazon is made by Champion.

Liquid Chlorine Pool Shock - Commercial Grade 12.5% Concentrated Strength - 1 Gallon

Non-chlorine shock

Non-chlorine shocks are known as Oxidizing shocks or chlorine-free shocks. They contain no chlorine but instead use oxygen to remove contaminants from the swimming pool.

With this type of chlorine-free shock, you can usually swim in as little as 20 minutes after adding it to your pool. However, Oxidizing shock will not get rid of algae growth so you will need chlorine shock for that.

One of the most popular on Amazon is the In The Swim Chlorine-Free Oxidizing Pool Shock which comes in 24 handy 1-pound bags.

How long after shocking a pool can you test the water

can you swim 12 hours after shocking pool
- Testing the water after shocking

You can test the pool water using test strips, a liquid test kit or an electronic water tester to establish how long after you shock a pool can you swim. The general consensus is that the level of free chlorine should be below 5 ppm and ideally below 3ppm before swimming resumes.

You should leave the chlorine shock to work for at least 4 hours after shocking a pool before you first test the pool water.

You should keep the pool pump running after shocking.

To explain the different chlorine terms I have written a post to help – Free Chlorine vs Total Chlorine vs Combined Chlorine Explained

Pool Maintenance Course

When I first bought my house with a swimming pool, I knew nothing about cleaning and maintaining it. I was recommended Swim University’s Pool Care Handbook and video course so I bought it and have never regretted it.

It was probably the best money I spent that year as I have saved thousands by doing it myself.

What happens if you swim in a shocked pool?

Swimming in a pool that has just been chlorine shocked can be potentially dangerous (as opposed to oxidizing shock – see above).

Swimming before the levels described above are reached can potentially result in one or more of the following problems:

  • stinging eyes
  • skin irritations
  • potentially worse conditions such as lung irritation.

If in doubt, don’t swim! Test the water and only go in when the levels are correct.

Read my full post What happens if you swim in a shocked pool?

Can you over shock a pool?

Well in a way you can but in practice it generally just means that you will have to wait longer for the chlorine levels to reduce to a safe level before swimming in the pool again. Perhaps up to 48 hours.

If you have severely over shocked and have a vinyl liner the strong chlorine solution may bleach it.

You can help reduce the chlorine levels by adding sodium thiosulfate granules to the pool. You can buy this on Amazon – Pool Dechlorinator Sodium Thiosulfate Pentahydrate 15 lbs by Cesco Solutions

So the lesson is to follow the instructions and ensure that you only shock to the level recommended.

Warning

As with adding any chemicals to a pool, always add the chemicals to water, NOT WATER TO CHEMICALS.

In other words, if you will be mixing the shock solution in a bucket always fill the bucket with water first and then sprinkle in the shock. Do not put the shock into the empty bucket and then fill it with water.

How long should you wait to swim when adding other chemicals?

Although some of the other chemicals you may add to your pool are relatively harmless, at least when compared with chlorine, it is generally not a good idea to swim in the pool immediately after adding chemicals.

It is a good idea to wait at least 15-30 minutes for the chemicals to mix with the pool water so there are no “strong” areas for chemicals such as adding flocculant, algaecide, muriatic acid, pH plus or minus or clarifier.

When adding Calcium Chloride to raise calcium hardness levels it is normally recommended to wait longer than 30 minutes, perhaps at least four hours. Follow the guidelines on the pack to be safe.

Summary

In general, how long to wait to swim after shocking a pool, is that no one should swim in the pool for a minimum of 6 hours and up to 24 hours. This time can vary depending on the type of shock used and the free chlorine levels, which you should test to make sure it is lower than 5ppm before anyone swims, no matter how long it is since shocking the pool.

FAQs

Can I swim 12 hours after shocking pool

Normally 12 hours is plenty of time to wait after pool shocking before you swim although it can take 24 hours. To be completely sure you should test the chlorine level in the water first.

How long after adding bleach to pool can you swim?

Bleach is a very weak chlorine solution so you need to put plenty in a pool to shock it. You should be safe if you leave it for at least 4 hours but make sure you test the level of chlorine in the water first

When can you swim after shocking a saltwater pool?

How long to wait after shocking a saltwater pool is no different to shocking a chlorine pool. A minimum of 4 hours and often more than 12 hours. To be completely sure you should test the level of chlorine in the water first.