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How to Shock Your Swimming Pool

T here’s nothing more relaxing in the summer than swimming in your own backyard pool or laying on an inflatable mattress all day with a cool drink in your hand. Your kids can find a way to consume all the extra energy while getting a nice healthy tan. Plus, your parties have ceased being dull, as everybody finds it delightful to take their drinks and continue chatting next to a cool water oasis.

But all these can easily become inaccessible if you don’t take care of the pool. There’s no secret that, if you don’t do regular wall scrubbing and waterline cleaning, you may end up with a marsh in your yard that won’t only ruin the scenery but stink day and night. This is, of course, the worst-case scenario. But it doesn’t mean that, if the water seems clean, it truly is or that it is safe to swim in it. As explained, the responsible thing to do is to maintain your pool and shock it regularly. We will explain the steps in the following paragraphs.

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What Does Pool Shock Mean?

It is an essential maintenance step, and it implies pouring three to five times more chlorine or other shock substances into the water. This will raise the level of chlorine for a few hours and help destroy algae and bacteria. As the chemical levels are so high during this process, no one should enter the pool, as the chlorine can attack the skin.

Why Should You Shock Your Pool?

Many elements can cause chlorine to become unbalanced. The sun can lead to chlorine evaporation, while frequent use of the pool can run out the resources of free chlorine which will combine with human waste like skin, hair, and urine. This will eventually lead to a lower level of chlorine than recommended and create a favorable environment for microorganisms to develop and spread. Algae will grow on the walls and cover the waterline. To put it short, if you don’t shock it regularly, your pool will become unusable.

How Often Should You Do It?

If you are using it every day, you should perform complete maintenance once or twice a week. The methods have become more diverse today and, if you are not willing to spend hours skimming the leaves and cleaning the walls, you can leave this job to a robotic pool cleaner. Nevertheless, you will need to take care personally of the chlorinating operation.

While it is true that if you only take a bath occasionally you can push the super chlorinating job to once a month, we advise not to do it. It would be more difficult later to clean all the algae, which will multiply and grow larger if not killed on time.

Besides the weekly treatment, some other situations require super chlorinating on the spot:

  • Heavy rain or storms – They can increase the water volume considerably and, thus, make the report between water and chlorine disproportionate. Furthermore, a strong wind can carry debris, seeds, and algae and contaminate the water. This is why it is recommended to thoroughly clean the pool if a storm hit and apply chlorine treatments to restore the balance.
  • Severe drought – This is the other side of the coin. If extreme heat has caused the water to evaporate, you have once again an unbalance, so you will want to add more water and then test chlorine level. In most cases, you will need to add more.
  • Intense use of the pool – If you’ve had friends over or your kids have spent every hour of the day in the water for the past days, it’s time to add some extra chlorine and sanitize the water as it will be filled with skin cells, hair, and, who knows, maybe urine.
  • An unfortunate incident – Kids and pets cannot be held accountable for leaving feces in the pool so, if this happens, it’s time to get everybody out, clean the mess, and shock the pool to remove all the bacteria.

Keeping a good chlorine level isn’t enough to maintain a clean and safe pool. Read our article about keeping pool water balanced and find out what other parameters need to be measured and adjusted.

A plastic spoon containing chlorine spilled on a table Image

Pool Shock Types

If this is your first time super chlorinating the pool, then you may want to take your time and decide which sanitizer will fit your needs better. And even if you are a veteran in this matter, it won’t hurt to discover the alternatives to what you are using now. Who knows? They may make your work easier.

Here is a list of the most common disinfectants:

For fast, cheap treatments, pick calcium hypochlorite

This would work best for pools with a low water pH, as Cal-Hypo already has a value of 10.8. Moreover, it contains calcium, so you will want to use it only if you are not dealing with hard water, otherwise, it will make it even harder.

Nevertheless, it is a strong substance with excellent action against algae and bacteria. And is super cheap as well. The only disadvantage is that it tends to run its course faster than other sanitizers. It usually comes as granules and needs to be dissolved into the water before being poured into the pool. Plus, you will want to do this at night, as sun rays can make it dissipate quickly and mess up your treatment.

For long-lasting results, choose sodium dichlor

The secret of this substance is that it dissolves slower, so it is released gradually into the water. Just like the disinfectant from above, it comes in granular form and needs to be mixed with water before being poured into the pool. It doesn’t contain calcium, so it is more suitable for hard waters. Nevertheless, it is still based on Cl so you will want to apply it at night to keep it away from sun action.

If you are dealing with hard water, opt for lithium hypochlorite

You can determine if your water is rich in minerals and especially calcium by testing it. You can find a testing kit in pool shops or online. It will show you if your water needs more calcium or is already at the limit. If it is the second situation you are dealing with, lithium hypochlorite is the option to pick, as it is strong against microorganisms, but doesn’t put calcium into the water. However, it is expensive, and sometimes it can be a challenge to find it.

If you cannot wait, pick a non-chlorine solution

This is a good option for when you are in a hurry. As it doesn’t contain chlorine, it isn’t dangerous for the skin and eyes, and, usually, you can get swimming after 15 minutes. The disadvantage, however, is that it is inefficient against algae, so, if this is the issue you are dealing with, you should look for another product.

Woman holding a pool water test above a pool Image

How Much Pool Shock Should You Use?

Here comes the math part. But stay chill. It has nothing to do with logarithms and radicals. We just need to define some concepts first and then crunch the numbers to see how much sanitizer you should use according to your pool’s size.

Let’s start by clearing the chorine deal:

  • Free chlorine – You need a good amount of this, as it is the one able to act upon microorganisms and neutralize them. It is the active element in the water.
  • Combined chlorine – It is the Cl that got combined with other elements like skin, bacteria, algae, and others. It has become inactive and can no longer act upon water contaminants.
  • Total chlorine – Is the sum between the two elements from the above and shows how much Cl exists in the water at testing time.

Now that you have this clear, it’s time to get down to serious business. Remember that is important to determine correctly the right amount of disinfectant you will need. If it is too high, it will be dangerous to the skin, while if it is too low, it will be inefficient. So, follow the steps with care:

Step 1 – Test the chlorine levels

You can find one of these tests at a pool supply store or online, and they are usually pretty straightforward. Some of them use chlorine tablets to test the water and others use drops. Check on the box and use the test according to the recommendations.

Try one of our best digital pool water test kits and get more accurate results. They will help you determine pH levels, chlorine, and calcium, as well as determine the presence and proportion of other metals and minerals in the water.

1. Measure free chlorine level

Dip the test tube to a depth of around 1.5 feet and wait until it gets filled with water. Remove it and insert a dpd 1 tablet into the water-filled tube. Shake the test until the tablet dissolves and then compare the color of the water to the included chart. Write down the value.

2. Measure total chlorine levels

Keeping the same water, insert a dpd 3 tablet in the tube. Shake it and compare the newly obtained color against the chart. Write down this value as well.

3. Calculate combined chlorine level

Let’s assume that you have obtained a 1.1 ppm free chlorine level and a 2.4 ppm total chlorine level. To determine the combined Cl level, we will use the formula:

Total Cl = Free Cl + Combined Cl

Working the formula into our advantage, we would have:
Combined Cl = Total Cl – Free Cl = 2.4 ppm – 1.2 ppm = 1.2 ppm

Step 2 – Calculate the breakpoint

The breakpoint, as the name says, shows the level at which there is enough Cl into the water to break down the combined Cl. We can calculate it by applying the following formula:

Breakpoint = Combined Cl X 10 = 1.2 ppm X 10 = 12 ppm

Step 3 – Find out the desired change amount

It tells you how much you need the water to change in ppm to become balanced and safe. This value will be your guide when calculating the amount of Cl you need to pour in. Follow the formula:

Desired change amount = Breakpoint value – Free Cl = 12 ppm – 1.2 ppm= 10.8 ppm

Step 4 – Determine how much solution you need

To find out this value, you will need first to divide the volume of your pool by 10,000 gals. to find out the amount of solution it takes to alter the ppm value in 10,000 gals. of water. Let’s assume that your pool’s volume is 50,000 gal. By dividing it to 10,000 gals, you obtain the number 5.

Check on the back of the package to find the amount of product needed to change 1 ppm per 10,000 gallons of water. Let’s pick the value of 1.8 ounces.

Now all you need to do is use the following formula to find out how much Cl you need:

Total amount = Product needed X Pool volume X Desired change amount = 1.8 X 5 X 12 = 108 ounces

You can find the value in pounds by dividing it to 16. In our example, you would need 6.75 pounds of pool sanitizer to shock a 50,000 gallons pool.

If the pool is dirty, make sure you clean it before applying super chlorinating treatment. Find a top-rated robotic pool cleaner among our selection and start enjoying the advantages of having clear water with no effort at all.

Man pouring pool shock into the water Image

Shocking the Pool Step by Step

Now that you have everything prepared, it’s time for the shock treatment. Before starting, make sure to dress appropriately, and by this, we mean wearing long-leaved clothes and clothing items that are older and you wouldn’t regret getting them stained. Wear gloves to protect your hands.

Here is how the process follows:

Step 1 – Prepare the product

If it comes in granular form, use a 5-gallon bucket to dissolve it. Fill it with water up to 2 thirds and, only after, add the sanitizing product. You should use 1 pound of product per bucket and prepare 1 bucket at a time. Make sure to stir the solution gently and not splash it on your skin as it can produce burns. You should do this operation after sunset to avoid chlorine being inactivated by the sun.

Step 2 – Pour the solution into the water

Turn on the pool as you will need it to mix the product with the water. Then, pour the solution by moving around the pool’s margins. If you have calculated that you need more chlorine, prepare another batch until you use the recommended amount. Make sure to move slowly to avoid the substance getting on your clothes or skin.

Step 3 – Let it sit

Check how much the product needs to be left to act until it is safe for you to enter the pool. Follow the indications, otherwise, you may end up with an ugly rash. Usually, it needs to pass around 8 hours until the water is safe. Meanwhile, make sure to keep your kids and pets out of it.

If your water is looking dirty, you are most likely dealing with algae. Check out our article about how to deal with black algae and learn ho to get them out of your pool.

Pool maintenance equipment including a bucket, chlorine tablets, and a pool water test Image

Frequently Asked Questions

What should I do if I put too much shock in the pool?

This can happen if you haven’t calculated the necessary amount correctly. Nevertheless, it is an easy-solvable problem. You just need to leave your pool uncovered and let the sun dissipate the extra chlorine. Test again in a few days and if the chlorine level has become normal, you can invite your family back into the pool.

Can I shock the pool two days in a row?

If a storm, a heavy rain, or an unhappy bowel incident happened at only 24 hours since you’ve applied chlorine treatment, it is indicated to do it again, especially if you are planning to use the pool the following days. Nevertheless, this practice should be reserved for extreme situations only, as it can be difficult to obtain balance afterward. If kids are going to swim in the water, it is better to let one or two days to pass until you grant them access, as their skin is usually more sensitive.

Do I use shock or algaecide first?

These two operations usually don’t work well together as they tend to neutralize each other. Thus, it is recommended to apply chlorine treatment first and wait for the chlorine level to drop under five ppm. Only after you can pour algaecide in and expect good results.

If I keep the pool cover closed, can I shook during the day?

If your pool is placed somewhere where the sun doesn’t reach, you can try this and cover it really quickly afterward. However, even short exposure to the sun can reduce chlorine efficiency, so it is always a better idea to resume to after-dusk treatments.

Why is my water brown after shocking it?

This usually happens if the water is rich in metals. Iron and manganese can lend the water a brown nuance and even stain your liner. Fortunately, this is not an irreversible situation, and you can usually find the products in store for quick and complete cleaning.

The Bottom Line

If you follow all the steps we’ve listed above, it is impossible not to obtain a sparkless pool that is safe at the same time. Just pay a little attention when you do your math and have patience when pouring the substance in. Thus, you will avoid accidents and always obtain perfect chlorine balance. Moreover, remember not to hurry to jump in immediately. Let the chlorine act and settle and use a test to determine if it is time for a swim.

Lexie Thorne
Lexie Thorne
Lexie is the newest member of the team, previously working for a local business that sold, among other items, robotic vacuums. She takes a keen interest in the latest tech and considers herself to be a veritable tech geek. Using her connections, Lexie makes sure that she always talks to experts when putting together reviews and articles to ensure the information you read is reliable and makes a difference toward aiding you to better understand how automated devices for home use work.
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