How To Shock Above Ground Pool

To keep algae and other bacteria from growing in your pool, learning how to shock it is one of the most important things you can do as a pool owner. Pool shock is very crucial because it does not only take care of algae, but it also takes care of your health as well.

So, it is pertinent that you shock your pool regularly. Though it sounds like a sophisticated process, it is actually a very simple thing to do. It may not be that easy if you are new to the process, but with time, the whole process becomes a lot easier.

In this post, you will learn the necessary steps required to shock your pool. Before you start, ensure that you have the necessary equipment listed below:

  • Pool shock
  • Protective gear
  • Bucket
  • Mixer (turning stick)
  • Test kit

Once these items are ready you can go ahead and shock your pool following the steps below:

  • Determine your pool volume.

Knowing your pool volume is vital because you will use it to calculate the amount of shock to add to your pool. We assume that you know the volume of your pool before now.

However, if you still don’t know your pool volume or you have forgotten the figure, this article here will help you to figure it out. There is a section where we discussed how to calculate pool volume.

  • Put on your protective gear.

Before you start using the chemical, you need to protect yourself from any form of accident. Some pool shocks are very strong and can burn your skin.

So, cover up completely to protect yourself. Wear your eye goggles and nose mask to prevent inhalation of the chemical. Don’t forget your hand gloves. 

Once you are fully protected, you can move to the next step.

  • Read the manufacturer’s instructions.

It is not advisable to start using a shock without reading the instructions on the product. It is true that the instructions for the process are basically the same, but you don’t overlook some critical details.

Different manufacturers may use the same materials to produce the shocks, but with different concentrations. That’s why some manufacturers will tell you to dilute before adding it to the pool, while others won’t.

So, it is very important to pay attention to the details. Get the instructions because they are far more important than the ones you read elsewhere. 

  • Test your pool water.

To know the amount of shock to add to your pool, you need to know the amount of total chlorine, free chlorine, and combined chlorine in your pool. And you can achieve that without a test kit.

Your test kits will help you to know the total chlorine and free chlorine in your pool, as well as the amount of calcium present. This will help you to know the amount of shock to add, and also the type of shock to use.

Once you measure the total chlorine and free chlorine in your pool, you can get the combined chlorine by subtracting the free chlorine from the total chlorine.

Combined chlorine = Total Chlorine-Free Chlorine


Total Chlorine is the sum of all the chlorine present in the pool.

Free Chlorine is the amount of active chlorine that is ready to attack bacteria.

Combined Chlorine is chlorine that has reacted with the compounds in the pool and is no longer active for disinfection.

Once you know the amount of combined chlorine in your pool, you can then calculate the amount of shock to add. Check how to do the calculation in the next section.

  • Dissolve the shock in water.

Some shocks come in sandy or granular form, and it is not advisable to add them directly in that form. They can sink to the bottom and damage the surface. 

So, it is best to mix it with water first before adding it to the pool. Usually, you start with one pound. Fill your bucket to about two-thirds and dissolve 1 lb of the chemical in the water.

You may skip this step if the manufacturer says you can add it directly to the pool, or if it’s in liquid form and doesn’t need dilution.

  • Add the shock and wait.

Now that you have the solution ready, add it to your pool and watch it clear the pool.

Don’t add the shock in a spot. Move around the pool when adding the chemical to help for easy circulation. Then wait for about 6-8 hours.

  • Retest the pool.

After about 6 hours, you can retest the pool water to know the state of the pool.

How much shock do I put in my above-ground pool?

First, you need to measure the amount of free chlorine in the pool with a DPD kit. You can get the kit online or from pool stores.

To do that, you have to fill the DPD test tube by dipping it into the pool water to about 1.5 m depth. Ensure it reaches the tube’s fill line.

Add one free chlorine tablet and cover the tube with the lid. (Note that some kits use chlorine drops instead of tablets.) Shake until the chlorine tablet dissolves.

Compare the color of the water in the tube against the chart on the kit. Record the reading.

In the same manner, use a total chlorine tablet to find the amount of total chlorine present in the pool. Fill the test tube with water, add the total chlorine tablet, and shake until it dissolves. Measure the color against the chart and record the reading.

Then use the values to calculate the combined chlorine. The combined chlorine is the chlorine that has reacted with other compounds like ammonia.

Combined chlorine = total chlorine – free chlorine.

For example, if the total chlorine and free chlorine measured are 3.5 ppm and 1.5 ppm, respectively, the combined chlorine will be:

Combined chlorine = 3.5 – 1.5 = 2 ppm.

Remember, the combined chlorine shouldn’t be more than 0.2 ppm.

The next step is to find the breakpoint, which is the amount of chlorine needed to break the combined chlorine (compound) in the pool. You do this by multiplying the combined chlorine by 10.

Breakpoint = Combined chlorine x 10

Since the combined chlorine from our calculation is 2 ppm, the breakpoint will be:

Breakpoint = 2 x 10 = 20.

Remember, we already have some free chlorine in the pool water. So to find the actual amount to add to the pool, you need to subtract the free chlorine from the breakpoint.

Thus, the actual amount of chlorine change is:

Breakpoint – Free chlorine = 20 – 1.5 = 8.5 ppm.

Usually, on the pack of the shock, you will see the amount of shock required to raise the chlorine level by 1 ppm for every 10,000 gallons.

So, we are using 10,000 gallons as the standard for our calculation. 

Divide your pool volume by 10,000.

Assuming your pool volume is 30,000 gallons, you will have:

30000/10000 = 3

Then check the pack to know the correct amount of shock needed to raise the chlorine by 1 ppm.

Multiply the amount on the pack by the pool volume calculated and the actual amount of chlorine change.

Assuming it is written on the pack that you need 2.5 ounces to raise the amount by 1. From our own calculations so far, we will have:

2.5 x 3 x 8.5 = 63.75 ounces.

That means that you need to add 63.75 ounces of chlorine shock to the pool to break up the combined chlorine.

Remember, these figures are assumed figures. You need to do the test to determine the exact figures for your own pool.

What kind of shock do you use for an above-ground pool?

Using a regular chlorine tablet to shock your pool is not something you need to try out. There are different types of shock out there you can consider. 

The most common shocks you can use to increase the free chlorine in your pool are listed below.

Calcium Hypochlorite (Cal Hypo)

Popularly known as “cal hypo”, using this chemical is the cheapest and easiest way to shock your pool. Municipal water sources have been using it for ages for water treatment.

What you need to know about Cal Hypo

  • It contains about 65-75% chlorine.
  • You need to dissolve it in water before adding it to the pool.
  • You have to wait for about 8 hours or more after the shock before you can swim.
  • You must use it when the sun has gone down.
  • For every 1 ppm of free chlorine added to your pool, it adds up to 0.8 ppm of calcium. 

Lithium Hypochlorite

Though it is more expensive, it dissolves faster than calcium hypochlorite. Since it adds no calcium to your pool, it is the best product when the pool already contains a high amount of calcium.

What you need to know about lithium hypochlorite

  • It contains about 35% chlorine.
  • You don’t need to dissolve it in water before adding it to the pool since it dissolves faster.
  • Use it when the sun has gone down.
  • You can only swim after 8 hours of use.
  • It is very active and can be toxic to aquatic life.
  • It is rare to find due to the high cost of production.

Sodium Dichloro-s-triazinetrione (Dichlor)

Popularly known as dichlor, it is very easy to use. With some brands, you can add them directly to your pool.

What you need to know about dichlor

  • It contains 50-60% chlorine.
  • It can be used as a chlorine sanitizer.
  • You can add it directly to your pool or spa, depending on the manufacturer.
  • For every 1 ppm of free chlorine added, it adds about 0.9 ppm of cyanuric acid.
  • Use it after the sun has gone down.
  • Swim after about 8 hours of use.

Non-chlorine shock

Non-chlorine shock, like potassium peroxymonosulfate, is a cheap and fast way to shock your pool. You can start swimming immediately after the shock.

What you need to know about non-chlorine shock

  • You can swim after about 20 minutes of use.
  • You can’t use it to clear algae in your pool because it doesn’t contain chlorine.
  • It can be added directly to your pool.

When should I add shock to my above-ground pool?

The time to add shock to your pool depends on different factors, like frequency of use, weather conditions, season, etc. So, no one can say this time or that time is the best time to add shock to your pool.

However, you need to be regular with shock treatment because algae don’t waste time when they see the opportunity to invade your pool. It is good to shock your pool weekly, at least once a week if you are a regular user. 

If you use it occasionally due to busy schedules, do your best to shock at least once every two weeks. But it is better if you can do it once a week.

Anyway, as we stated above, there is no timeframe for shock treatment. The goal is to keep your pool free of bacteria and pollutants. To achieve this, you need to pay attention to some factors. The most common ones are:

  • Pool party: a lot of bacteria can enter the pool from the bodies of the swimmers. More so, the chemicals and sweat from the body will affect the chemical balance of the water and chlorine level as well.
  • Heavy rain: heavy rainfall can affect the chlorine level in your pool. So, do your best to shock your pool after a big storm.
  • Bowel-related incidents: this can introduce bacteria into the pool water. The best thing to do is to shock the pool immediately to kill any bacteria in it.
  • Chlorine odor: chlorine odor indicates that there is a high level of combined chlorine in the water. Shock the pool to break up the combined chlorine molecules.
  • Before closing the pool for winter: you can’t close your pool for winter without shock treatment unless you want to breed algae in it. Shocking the pool will help to limit the amount of algae that will enter the pool.
  • After opening the pool: after leaving your pool for a long time, it is normal that algae will find its way into the pool. So, always shock the pool before you start using it.

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