Pool Care Pool Water Chemistry

Here’s How to Shock Your Swimming Pool in (10 Steps)

If you’re hearing about pool shock now, then you might think you’ll be electrocuting your swimming pool. But it’s nothing about that at all. Or you might be familiar with the term, but you don’t know what it entails.

Pool shock is one of the maintenance routine practices you got to give to your swimming pool to make it swimmable and safe.

The good news is, I have compiled everything there is to know about pool shock in this post just for you. Read along!

What is Pool Chock?

Pool shock, or rather, pool shocking, is the process of adding chlorine or non-chlorine sanitizing chemicals to your pool. The aim is to raise the “free Chlorine” level in the pool water to give the sanitizer extra strength to destroy algae, bacteria, and chloramines.

But what are these chloramines? If your swimming pool has a strong chlorine smell, it doesn’t; it is clean. A clean swimming pool should odor-free. If yours has a strong smell, it’s an indication you need to treat it by shocking.

The smell is from the extra chloramines or rather the combined chlorine. It’s formed when the free chlorine in the pool water mixes with nitrogen from oils, sweat, and urine.

Apart from making your pool smell, these chloramines can also cause skin, eye, and respiratory stem irritation.

When you shock your pool, you add enough chlorine or other pool chemical with enough strength to clean your pool water and destroy the chloramine buildup.

The whole process is known as super-chlorination.

Why shock your pool?

Shocking your pool helps remove the combined chlorine molecules. It’s a way to eliminate the excess swimmer waste and any bacteria that might be resting in your swimming. It’s necessary after heavy pool use, algae infestation, and contamination events like rain.

If your swimming pool is a bromine-treated type, pool shocking will help reactivate the bromide ions inside the water.

Pool shocking required you to raise the chlorine levels high enough, around 10 – 30 ppm, to oxide and destroy the pool contaminants.

Here are the three main reasons for shocking your pool, the ABCs of pool shock:

A – Algae

Algae is a nasty contaminant that can cause a series of pool issues. It comes in green, yellow, black, and rare pink.

The best solution to getting rid of algae is using a robust algaecide. And you know what, nothing can beat chlorine as the best algaecide.

Even though you can control pool algae growth with algaecide, you can only kill them and clear your pool by shocking it.

You need around 10-30 ppm of chlorine to kill the active algae blooms, depending on the algae severity.

Chlorine accelerators boost the chlorine level making the sanitization strength potent to kill severe algae bloom of all types and colors.

B – Bacteria and Bather Waste

Pool bacteria can get into your pool water from various sources. Most of the pool bacteria are harmless, but some are pathogenic.

It would be best if you shocked your pool to get rid of the bacteria after heavy use, heavy storm, or an extended winter. Things included in the bather waste have hair, skin, soaps, sweat, urine, feces, cosmetics, and fungus.

C – Chloramines, Cloudy Water, and Contaminants

When combined chlorine molecules form in your pool, they may cause skin, eye irritation and produce a strong chlorine smell. That is when the chloramine levels go beyond 0.5 ppm.

At this point, the only way to deal with the problem is to add enough chlorine or non-chlorine shock. It will help break the chloramine molecules apart.

DPD test kits test for both Free and Total Chlorine. The difference between the two values gives you the combined chlorine. Shocking is necessary when the level of the chloramines exceeds 0.5 ppm.

Apart from getting rid of the chloramines, pool shocking can also help clear your pool water. If you have a cloudy pool after cleaning, shocking it would leave you with crystal clear water.

Other reasons why you should shock your pool include:

Close-Down and Start-Up

If you live in those cold areas, you’ll need to close your pool during the winter and reopen it in the summer.

During the closing time, you need to chock your swimming pool to give chlorine enough strength to protect it from algae and bacteria during the nap.

It’s a process you’ll have to repeat during the pool startup. The process helps eliminate any algae that might have found a way to grow during the closed period.

Heavy Rain

You might know rain as pure water distilled by evaporation. However, when falling from the sky through the air, the water particles pick up some airborne contaminant particles deposit them in your pool water.

Contaminants brought in by rain such as dust, algae spores, and pollen can cause cloudy water, consume the sanitizer and affect your pool water chemistry.

What’s more, those overhanging trees, heavy storms, or overflowing planters can bring bacteria and phosphates into your swimming pool, not forgetting tree and plant debris.

Super-chlorination will help eliminate the bacteria, algae spores, and other contaminants after cleaning your pool.

Extended Hot Weather Periods

The water temperatures might rise above the optimal pool temperature during the scorching summers, ranging between 78°F – 82°F. It makes it easy for algae and bacteria to grow and thrive.

What’s more, the sun UV rays decrease the amount of chlorine in the pool lowering the guard against these bacteria, algae, and contaminants.

Heavy or Frequent Pool Use

Chlorine levels will reduce quickly when more swimmers use your pool or when used frequently. What’s more, when you hose a pool party, all the wastes, including sweat, could form chloramines. That’s why it’d be best to shock your pool after such an event.

When is the Best Time to Shock Your Pool?

Of course, timing is a crucial factor when shocking your swimming pool. Can you shock a pool any time of the day?

No! You cannot shock your pool any time of the day. As I mentioned earlier, sun UV rays affect chlorine’s effectiveness, and that’s why you have to avoid shocking your pool during the night.

The best time of day to shock the pool is at night. At this time, the pool temperatures are optimal, and there is no sunlight to interfere with the pool shock effectiveness.

What’s more, the risk of somebody accidentally getting into the swimming pool when super chlorinated is lower.

What Types of Pool Shock Can You Use?

You cannot super-chlorinate your swimming pool with regular chlorine tablets. Thankfully, if you’re open to options, there are types of pool shocks you can use to treat your pool water.

Calcium Hypochlorite

Cal Hypo, as known by many, is the most popular type of pool shock. It’s been used to disinfect and treat swimming pools and city or municipal water sources for decades since 1928. It’s also the cheapest and most convenient way you can shock your pool water.

Its Features

  • Adds about 0.8 ppm calcium for every one ppm Free Chlorine added
  • Most of its commercial versions contain 65% – 75% chlorine
  • Requires to be dissolved before adding it to pool water
  • Requires 8-hours roughly before a safe swim
  • Must be used after dusk

Lithium Hypochlorite

If your pool capacity is enormous and your budget allows you to pay extra, Lithium Hypochlorite is your best option.

It dissolves faster compared to Cal Hypo. That allows you to add it to your pool water directly – no need for dissolving it first.

However, it’s becoming a rare product since pool chemical manufacturers are halting their production due to the high lithium costs.

Its Features

  • Requires around 8-hours before a safe swim
  • Commercial versions contain 35% chlorine
  • Toxic to aquatic life thus a solid algaecide
  • Must be used after dusk

Dichlor (sodium dichloro-s-triazinetrione)

Dichlor, available as sodium dichloro-s-triazinetrione or dichloroisocyanuric acid, is another pool chock you can use. However, you might want to be the last option on your list for its complex use. The method of application depends on the brand.

Its Features:

  • Ideal for both pool shock treatments and regular chlorine doses
  • Adds around 0.9 ppm cyanuric acid in every ppm additional FC
  • Requires roughly 8- hours for a safe swim
  • It can be added directly without dissolving
  • Contain 50% – 60% chlorine
  • Used after dusk

Non-Chlorine Pool Shock

If you’re not a fan of chlorine, then non-chlorine pool shock is an option for you. One of the most popular non-chlorine pool shocks uses potassium peroxymonosulfate. It’s fast and budget-friendly. That makes it an excellent choice if you need to shock your pool and swim soon afterward.

Its Features:

  • It can be added directly to the pool water and any time of the day
  • It cannot be used as algaecide since it doesn’t have chlorine
  • Requires roughly 15-minutes to enjoy a safe swim

How to Shock Your Pool (Step by Step)

Now that you’re familiar with what pool shock is, it’s time to get handy and experience the practical part. It’s a simple process when you follow the steps to the bar.

If you’ll be using chlorinated pool shock there, one thing to remember is, the best time of the day to shock your pool is when the sun goes down.

Another thing, pool chemistry must be balanced, especially water pH and Cyanuric acid. These tend to get in the way of chlorine efficiency.

What Amount of Chlorine Shock Do You Need?

Before you can start shocking your pool, you’ll need to estimate the right amount of pool shock to use and requires you to calculate your pool’s volume.

You can do all the calculations, but there is a quicker way around it. You can use an online pool calculator to figure it out. But if you like doing things your way, I have some formulas you can use for the calculation.

Knowing the right amount you need will ensure your pool shock is effective and prevent you from overspending.

Square or Rectangular Pools with Constant Depth

Length x width x depth x 7.5 = volume (in gallons), with 7.5 being the number of gallons in each cubic foot.

Square and Rectangular Pools with Variable Depth

Length x width x average depth x 7.5 = volume (in gallons)
(Deep end depth + shallow end depth)/2 = average depth

Circular Pools

π (3.14) x radius squared(r2) x average depth x 7.5 = volume (in gallons)
In short form: π x r2 x average depth x 7.5 = volume (in gallons)
(Deep end depth + shallow end depth)/2 = average depth
Radius = the distance across the pool top/2
π = pi, a mathematical constant.

Kidney or Irregular Shaped Pools

You can use Length × Width (average) × Depth (average) × 7.5 for smaller pieces and then add them up.
Or 0.45 x (A+B) x length x average depth x 7.5 = volume (in gallons)

How to Determine the Pool Shock Amount to Use

Now you know the pool volume, what next? According to experts, the right amount of chlorine shock to use in your pool is:

If you’re using liquid pool shock (sodium hypochlorite), you’ve to add around 10 ounces for a 10,000-gallon pool. That will raise the free chlorine (FC) by one ppm.

So, if your pool capacity is 50,000 gallons, you need (50000/10000) x 10 ounces = 50 ounces of sodium hypochlorite.

If you use calcium hypochlorite or rather a pool shock powder, you need 1-pound powder for every 10,000-gallon swimming pool.

If your pool has algae, you need a triple-shock dose, thus requiring you to add 3-pound powder for every 10,000 gallons of pool water.

How to Shock Your Pool (Step by Step)

Now that you’re familiar with what pool shock is, it’s time to get handy and experience the practical part. It’s a simple process when you follow the steps to the bar.

If you’ll be using chlorinated pool shock there, one thing to remember is, the best time of the day to shock your pool is when the sun goes down.

Another thing, pool chemistry must be balanced, especially water pH and Cyanuric acid. These tend to get in the way of chlorine efficiency.

What do you need?

  • Protective eyewear
  • Chemical-resistant gloves
  • A Disposable Pants and a long-sleeved shirt
  • Liquid testing kit or Water test strips
  • Wooden stick or a stirring stick
  • Pool Shock (of your choice)
  • A 5-gallon bucket
  • Closed-Toe Shoes

Steps to Follow:

Step 1: Put on the safety and protective gear before anything else.

Step 2: Test your pool water for Free-Chlorine and Total Chlorine using your preferred testing kit to determine the amount of Combined Chlorine in your pool water. It’ll help you realize the amount of pool shock needed.

Step 3: While testing for FC and CC, check how balanced the pool water is before proceeding. The water pH and alkalinity have to be balanced before you can shock it.

Step 4: If your pool water chemistry isn’t balanced, work on that first. If balanced, you can skip to the next step.

Step 5: Read the pool shock product manufacturer’s instructions carefully. At times, the package would also come with a chart or charts to help you determine the amount of pool shock you need.

Step 6: If the information isn’t available, you will have to calculate it yourself here.

  • Take the FC value and subtract the TC value from it to get the CC.
  • Multiply the CC value by ten.
  • Then subtract the FC value from the answer you got.
  • Check the owner’s manual for the amount of pool shock you need to produce a chemical change of 1 ppm in 10,000 gallons of water.
  • Take your pool volume and divide it by 10,000 gallons.
  • Multiple the one ppm chemical change by the value you got and the value you got for CC x 10 – FC.
  • Covert your answer into pounds by dividing it by 16 – the result you’ll get is the amount of pool shock you need.

Step 7: If your pool shock needs to be dissolved first before use, take the 5-gallon bucket and fill it with warm water, roughly ¾ full. If your pool shock doesn’t need to be dissolved, skip to step 10.

Step 8: Slowly add the shock to the bucket and use the wooden stick to stir until all the chemical dissolves. Start with one pound and increase it slowly until saturation.

Step 9: Pour the shock solution into your swimming pool slowly as you walk around it to give it an even distribution. If there some shock particles at the bucket bottom, dip them into your pool water and swish them around carefully to dissolve them.

Step 10: If your pool shock doesn’t need to be dissolved, check the containers’ capacity and calculate how many you need. Add one bag at a time.

Is your pool still green after shock and algaecide? Or is your pool water cloudy after aftershock? Don’t worry, give it time. Pool shock is the ultimate treatment for such problems. You can add a water clarifier to fasten the clearing process.

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

Now you can wait for the pool shock to do its work. The shock package will typically have information on the amount of time you need to wait.

It might irritate your eyes, breach your hair and swimsuit or cause skin irritation. If the information isn’t there, I have you covered in the next section.

Check the manufacturer’s recommendations on how long you should wait before swimming again. You don’t want to feel the aggressiveness of chlorine.

Typically, you have to wait for at least 8-hours for the chlorine-based treatments. But if you used a non-chlorine pool shock treatment, you only have to wait for 15-minutes.

If you want to be sure if your pool water is safe for swimming, test for the free chlorine and make sure it’s less than three ppm. If you’re in a hurry, you can use a chlorine reduction agent.

How Often Should You Shock a Pool?

You don’t wait until your swimming pool starts to smell or when your eyes start itching to shock your pool water. It’d be best to shock it at least weekly to keep its water chemistry adequately maintained.

The more you use your swimming pool, the more you should keep its water balanced and adequately shocked. Apart from shocking it weekly or semi-weekly, it’d be best to give it extra pool shock treatment is certain occasions like:

  • After a heavy pool use
  • A severe rainstorm
  • A damaging winds
  • A major water refill

Giving it the extra shock treatment protects it against algae, bacteria, and other contaminants that might have found their way into your pool water during the event.

How Long Does Pool Shock Last?

Since pool shock is a human-made chemical product, it has a shelf life. You must understand how long it’ll last to know if it will be viable next time you need to shop your swimming pool.

Granular chlorine pool shocks lose only a tiny potency percentage when you store them in a recommended cool, dry, and dark place.

However, if you store them in a shed or garage with varying temperatures and humidity, the granules start to solidify. In few years, your pool shock quality will deteriorate.

If you need extended and safer storage, it’d be best to go for loose Cal Hypo in a bucket or use non-chlorine shock.

Storage must be in a cool, dry, and dark place and the bucket lid must stay tightly closed to prevent moisture and contaminant from getting inside.

Pool Shock Safety

Pool Shock Usage

When using your pool shock, use scissors to cut the bag carefully and slowly pour the content into the water. Using a pool brush, distribute everything and make sure you sweep or wash the spills into the pool.

If you’re shocking a vinyl liner pool, pre-dissolve your granular pool shock, that is, if you’re not using the quick dissolving Oxy Shock.

Never use anything other than water for dissolving your pool shock. Pool shock is reactive, and if you mixed it with another substance, it might explode, ignite or release toxic gases.

Another thing, you must NEVER add your pool shock into the chlorinator, skimmer, or floater. Always add it directly to the pool water.

Before starting the shocking process, wear protective gear, including chemical-resistant gloves and goggles.

Try your best not to breathe directly into the pool shock container. Exposure to chlorine irritates the breathing system, throat, and lungs. You can wear a dust mask or get a chemical mask if you want to feel safer.

Pool Shock Storage

Store in a cool, dry place away from other chemicals. Keep it out of reach of children too. Never store half-used or opened pool shock; it might spill, get contaminated or absorb moisture.


Well! Is it hard as first seamed? Shocking your pool is a straightforward process that requires nothing but your discipline in handling chemicals. Other than that, everything is a walk in the park. And as you well know, this is a section of the whole pool maintenance process. So, take a step and check out my posts on pool algae control, closing and opening your pool, and much more.

About the author

Sharif Miah

Hi! I'm Sharif, the founder of Globo Pool® and I have been working in the pool & hot tub industry for the last few years. I love to share my experiences with people & hope you are enjoying my information and lessons!

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