How do you shock your swimming pool

This is how you carry out the pool shock scorching correctly

Last updated: April 28, 2021

Whether you're a new pool owner or an old hand, shocking your pool can be a little scary. That's okay - handling such a large amount of chemicals can make anyone nervous. With practice and knowledge, it gets easier.

Once you've learned what pool shock is, why it's one of the most important chemicals, and how to shock a pool, the whole process will feel pretty routine. That's a good thing, because regularly shocking your pool is an easy way to prevent algae and bacteria from settling in the water. It also helps keep your pool from smelling like nothing ... well, hopefully nothing.


What is Pool Shock anyway?

Remember the last time you walked past a hotel pool. The chemical smell probably knocked you off your feet, right? You might think the distinctive smell is chlorine, but the smell is from chloramines, a sign of improperly balanced water.

Chloramines form when the chlorine in your pool mixes with the nitrogen in sweat, oils, and urine (we're sure it's not in your water, although we can't vouch for the hotel). This is a natural chemical process, basically a by-product of your chlorine doing its job.

In addition to making your pool smell unpleasant, too many chloramines can also irritate your skin, eyes, and respiratory tract.

By shocking your pool, you are adding enough chlorine (or another chemical) to purify the water and destroy the accumulation of chloramines. This process is also called superchlorination.

Pool chlorine 101

Before we dive into how to shock a pool, you must first understand the difference between total and free chlorine, and what combined chlorine and breakpoint chlorination are.

Free chlorine (FC) is the amount of chlorine that actively disinfects your water. You want the FC of your water to be between 1 and 3 parts per million (ppm) for the chemical to do its job.

Combined chlorine (CC) is the chlorine that has already been used. It's still in the water, but its disinfecting power is greatly diminished. You should keep your CC level below 0.2 ppm.

The total chlorine (TC) is the sum of the FC and CC in your pool.

Pool water test kits can measure the FC and TC of your water. To determine the CC value of your pool, you simply subtract the FC value from your TC value.

Breakpoint chlorination is when you have enough FC to break the molecular bonds of chloramine. You need to add ten times the amount of CC to get to this point.

Every time you shock your pool, try to hit the breakpoint. Failure to hit the breakpoint can lead to even more chloramines in your pool, and if chloramine levels continue to rise uncontrollably, you may have to replace some or all of your water to fix the problem.

Types of swimming pool shocks

You can't usually shock your pool with your regular chlorine tablets, but you have a choice of different products when it comes to increasing chlorine levels.

Calcium hypochlorite

Also known as Cal Hypo, this chemical has been used to disinfect swimming pools and municipal water sources since 1928. It's one of the cheapest and most convenient ways to shock your pool.


  • Most commercial versions contain between 65% and 75% chlorine.
  • Calcium hypochlorite needs to be dissolved before adding it to your pool.
  • It must be used after dark.
  • It will be about eight hours before you can swim safely again.
  • It adds about 0.8 ppm calcium to your water for every ppm FC, so be careful if your water is already high in calcium.

Lithium hypochlorite

If your water is high in calcium and you don't mind paying a little extra, lithium hypochlorite is the way to go. It dissolves much faster than calcium hypochlorite, so you can add it straight to your pool without dissolving it first.


  • Commercial versions contain 35% chlorine.
  • It must be used after dark.
  • It takes about eight hours before you can swim safely again.
  • It can be toxic to aquatic life (making it a solid algicide), so you need to be careful when disposing of the recently treated water.

Note: Lithium hypochlorite can be difficult to find. Some pool chemical manufacturers have stopped manufacturing because the cost of lithium has increased and most of it is now used to make lithium batteries.


The actual names of this pool shock chlorine are sodium dichloro-s-triazinetrione or dichloroisocyanuric acid. (Try saying one of these five times quickly.) Dichloro Shock is much easier to pronounce and even easier to use. Depending on the brand, you can also add it directly to your pool.


  • It usually contains between 50% and 60% chlorine.
  • You can use it for both normal chlorine dosing and shock treatments.
  • Usually, you don't have to resolve it beforehand.
  • It adds 0.9 ppm cyanuric acid for every ppm extra FC.
  • It must be used after dusk.
  • It will be about eight hours before you can swim safely again.

Non-chlorine shock

If you want to shock your pool and swim again shortly afterwards, this is for you. The chlorine-free shock with potassium peroxymonosulfate is a quick and inexpensive alternative to pool shock.


  • You can always add it directly to your pool water.
  • It takes about 15 minutes before you can swim safely again.
  • Since it is not based on chlorine, it does not work as an algicide.

When to shock your pool

You may have noticed that the instructions on the chlorine shocks say they must be used after sunset. That's because the sun is burning away unstabilized chlorine, which means the shock is no longer as effective. Shocking your pool at night will ensure that the chemicals work as they are intended.

How often should you shock your pool

You don't want to wait for a bad smell or itchy eyes to appear before shocking your pool. We recommend that you shock your pool once a week or at least once every two weeks to keep the water chemistry right. The more you use the pool, the more often you should reach for the pool shocker.

In addition to your weekly or biweekly treatments, you should perform an additional pool shock under certain circumstances, e.g. after:

  • heavy pool use (like a pool party)
  • a heavy rainstorm or noxious winds (especially if there is debris in your pool)
  • a big change in the water level
  • an accident related to the bowels in the pool

Think of extra shocks as insurance against breakdown algae and other contaminants. It's better to get rid of all the bacteria before they have a chance to affect the quality of your water or make someone sick.

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How to shock a pool

You have the chemical knowledge. Now is the time for the hands-on experience. Super chlorinating your pool is shockingly (sorry, we couldn't resist) easy once you get the hang of it.

Important! Remember, if you are using chlorinated pool shock, wait for the sun to set before adding it.


  • safety goggles
  • Chemical resistant gloves
  • Pants and long-sleeved shirt (which you must not get dirty)
  • Closed toe shoes
  • Water test strips or fluid test kit
  • Shock medication of your choice
  • 5 gallon bucket (if you need to dissolve the pool shock before adding it to the water)
  • Wooden stick (to stir to dissolve the water)

Before you begin, you need to calculate the volume of your pool. If you don't know how much water your pool holds, you can use this pool calculator to find out.

Pool volume calculator

First choose the shape of your pool.




1) Put on your protective clothing.

2) Do a quick round of FC and TC pool water tests to determine how much CC is in your pool. This measurement determines how much pool shock you need.

3) Carefully read the manufacturer's instructions on your shock product. Most packages contain tables or steps to help you calculate how much shock you need. If you have to calculate it yourself:

  1. Subtract the FC from the TC to find the CC.
  2. Multiply the CC by ten
  3. Subtract the FC from this sum
  4. Find out how many ounces of shock cause 1 ppm chemical change in 10,000 gallons of water
  5. Divide your pool volume by 10,000 gallons
  6. Multiply the chemical change by the shared pool volume and the CC / FC difference
  7. Convert the answer to pounds by dividing by 16. The result is the amount of pool shock you have to use

4) If you need to release the shock first, fill your bucket about 3/4 full with warm water. Otherwise continue with step 6.

5) Put the shock in the bucket and stir slowly until the chemical is dissolved as much as possible. Work in one pound increments. Go to step 7.

6) If you don't need to release your shock, count how many containers of shock you need. Add one bag at a time until you reach your calculated breakpoint.

7) Pour the shock in slowly as you walk around your pool for a more even distribution. (If your shock-water mixture has solid particles on the bottom, submerge the bucket in your pool water, gently swirl it over to dissolve it, and keep pouring).

8) Wait to use your pool depending on when you added the shock and the manufacturer's recommendations. You don't want to irritate your skin and eyes or fade your swimwear.

Pool shock safety

Shocking your pool is a necessary part of good maintenance, but please be aware that these chemicals can be extremely dangerous if handled incorrectly. We're not exaggerating the danger - improperly stored chlorine can literally explode.

Always wear protective clothing - especially safety glasses and chemical-resistant gloves - when handling and dissolving chlorine. Pool shocks, especially calcium hypochlorite, can sometimes release small amounts of chlorine gas. Wearing protective clothing can help prevent eye and skin irritation.

Do your best to avoid inhaling directly from the containers. Exposure to chlorine gas can cause irritation to the throat and lungs. You probably don't need a dust mask, just try not to breathe too close to the container. However, if you feel more confident, you can use a chemical mask.

Never, ever mix types of pool shocks. We don't want you to become a science experiment gone wrong. Mixing liquid chlorine or even dry chlorine granules can cause a volatile reaction. Add each chemical to your pool separately.

Do not apply the shock directly to the pool water unless directed to do so. If the package says you should dissolve the product before adding it, do just that.

Open only one container at a time. If you need to use more than one container of shock, make sure to completely empty each container before moving on to the next.

Don't be shocked, you did it!

Now you know why, when, and how to shock a pool. A little math might be included, but aren't the occasional brain teasers good for your memory anyway? We're pretty sure that's true, but maybe we've forgotten.

However, whatever you think about the math, using pool shock regularly can prevent more work in the long run. It's one of the easiest ways to keep bacteria at bay, keep your water clear, and enjoy your time in the pool.