I have been involved with swimming pools and water treatment for a long time. As a kid, I took to the water and never looked back. Through my teenage years, I was associated with the Miami Biltmore Hotel, where I worked as a part-time pool boy and a swimming instructor. It was here that I was initiated into the world of water treatment. So when I  started WaterMan, a water treatment company, with a friend, our focus was on helping local pool owners maintain the hygiene of their pool.

The need to keep your pool clean, safe and sanitary is important not only for you but for anyone who may be using the pool. As a pool owner, it is your responsibility to keep the water safe to swim in. So if there are algae floating in the pool or different microbes are using your pool as a hub for reproducing and spreading disease, it is a problem you have to nip in the bud. But it doesn’t have to be a daunting task if you maintain your pool chemical readings and carry out regular shock treatments.

In the following article, I will take you through the details of what it means to shock your pool and how you should go about doing it safely.

What Does ‘Shocking’ Your Pool Even Mean?

When you hear ‘shocking’ your pool, it sure sounds scary. But shocking your pool doesn’t have to be as complicated or in the least bit scary if you do it right, and with care. First, let me clarify there is no actual electricity involved, so if you thought you had to mix water and electricity (something you have been told to never do since you were a child), you can rest assured. Shocking your pool simply means you give the water a jolt with chemicals so the system can be reset. It ensures the impurities are killed and the water is clean and safe for you to swim in.

Shocking your pool typically involves putting at least three times more the normal amount of chlorine and other sanitizers. When the chlorine in the pool mixes with bodily fluids like sweat and urine (it happens more often than you think), a chemical compound called chloramine is formed. Chloramines forming in your pool is a sure shot sign that the chlorine is working and is killing impurities. But when too many chloramines are formed, the water needs to be shocked in order to diminish the buildup of chloramines. Too many chloramines can cause irritation to your eyes, skin, throat, etc. Therefore, to strike a balance you need to shock your pool.

Free and Total Chlorine

Before going into further details about shocking your pool, you need to understand the nature of chlorine that is used in your pool and how it works. There is a key difference between free chlorine and total chlorine. The following are some definitions you may want to keep in mind:

  • Free Chlorine: Free chlorine is the chlorine that is at work actively to disinfect the water. Ideally, the reading of free chlorine in your pool should be between 1 and 3 parts per million (ppm).
  • Combined Chlorine: Combined chlorine is the chlorine that the water has already absorbed for sanitation. It is, however, still in the water but is not serving any purpose as a sanitizing agent. The CC level should be less than 0.2 ppm at all times.
  • Total Chlorine: Total chlorine, as you may have already inferred, is the sum of the free chlorine and the combined chlorine.

When you use a chemical test kit on your pool, you can find out the total chlorine and the free chlorine present. To find out the combined chlorine, you have to subtract the amount of free chlorine from the total chlorine (TC-FC).

The idea of shocking your pool, therefore, is to bring the free chlorine levels to a point where you can break down the amount of chloramine present in the water. The point when there is enough free chlorine to break down the chloramine in the water is called breaking point. Each time you shock your pool, you must attempt to reach this point. If you are not able to balance the chloramines out in time, then you may have to replace the water altogether.

Shocking Your Pool

Now let’s come to the main point — what does shocking your pool entail? You need more chemicals than simply the chlorine tablets you have been using.

The general readings for your pool should be:

  • Chlorine:0 – 3.0 ppm
  • pH:4 – 7.6
  • Alkalinity: 80 – 140 ppm
  • Calcium Hardness: 200 – 400
  • Cyanuric Acid: 25 – 50 ppm
  • Total Dissolved Solids: 500 – 5000 ppm

But when you shock your pool, the levels are generally elevated. There are a few different kinds of shock you can work with, depending on availability and requirement.

Types of Shock

The following are some common types of shocks available in the market:

Calcium Hypochlorite

Calcium hypochlorite, or cal hypo as it is commonly known as is a popular way to disinfect pools. It’s available easily and does not cost too much money either. It typically contains about 65-75% chlorine and needs to be dissolved in a bucket before you can add it to the water. For every ppm of free chlorine, it also adds about 0.8 ppm of calcium. So if you live in an area where the water is hard, the calcium makes the water even harder. Cal hypo will also increase your pH level but that can be balanced easily.

It takes about eight hours to dissolve before you can swim in the water again safely.

Lithium Hypochlorite

If your water is already high in calcium content, you can always choose to go with lithium hypochlorite. It can be poured into the pool directly, without needing to be dissolved beforehand. It also dissolves much quicker than calcium hypochlorite. It contains approximately 35% chlorine. Again, you need to wait at least eight hours before you swim in the water again. If you are disposing of water that has been treated with lithium hypochlorite, you need to be careful as it can be toxic to some marine life. So it should not mix directly into your sewer water.


Dichlor shock or dichloroisocyanuric acid is extremely easy to use and can mostly be added directly to the water (read the instruction manual carefully). It has about 50-60% chlorine and can be used both as shock treatments and regular chlorine doses (but the proportions will differ). For every ppm of free chlorine, it adds about 0.9 ppm of cyanuric acid.

Non-Chlorine Shock

If you want to swim immediately after shocking your pool, you cannot use a chlorine-based shock. With a potassium peroxymonosulfate shock treatment, you can swim within 15 minutes of shocking your pool. It can be added to the water directly without any concerns about whether it will dissolve. It is also quite inexpensive if you have to buy it frequently to shock your pool. However, if you have algae, perhaps you need to stick to a chlorine-based shock treatment as potassium peroxymonosulfate will not kill algae.

Instructions to Shock Your Pool

Here’s how you should ideally go about shocking your pool, though some steps may differ depending on the shock treatment you are using and the manufacturer’s instructions:

  1. Make sure you have your protective gear on — this includes gloves, safety glasses, etc.
  2. Do a chemical test to see what your numbers are. Determine your combined chlorine content by subtracting free chlorine from total chlorine.
  3. Read the instruction manual to see how much shock the pool needs according to the combined chlorine you have calculated.
  4. If the instructions require you to dissolve the chemicals first, do that in a bucket filled about 3/4th with warm water. Add the shock and stir carefully and slowly until it has dissolved.
  5. If you don’t need to dissolve the chemicals, figure out how many containers of the shock you will need to reach the breakpoint. Add the bags one at a time.
  6. Ideally, you should walk around your pool as you pour the shock to get a more even mix.
  7. Let the treatment sit in the pool for at least eight hours or whatever amount of time has been dictated in the user manual. You may want to turn on the pump and filter so the shock is dissolved evenly.
  8. Do another chemical test before you jump into the water. If the balance isn’t right, take measures to fix it before you use the pool.

Important Things to Know

There are some things you will need to be careful about when shocking your pool. Safety comes first, so read the instruction manual very carefully before you handle the chemicals. Here are some tips you may find helpful:

  • Never handle the chemicals without your protective gear on. The shock is likely to release chlorine gas which could irritate your skin so do not touch the chemicals directly.
  • Try not to inhale the container of chemicals for too long. The chlorine gas could irritate your throat and lungs. You don’t necessarily have to wear a protective mask as long as you are careful.
  • If you are using different chemicals, do it one by one. Do not attempt to mix your chemicals as you may not be aware of the reaction it may cause. It could be dangerous and volatile.
  • When dissolving the shock, always add the chemical to the water and not the other way around.
  • Always do your treatment at night unless the instruction manual says it is alright to do it in the sun. The sun’s ultraviolet rays tend to burn off the unstabilized chlorine so it will interact with the sun even before it has the chance to do its job.
  • Use one container at a time. This will make sure you don’t end up opening more containers than you require as this would lead to trouble in storage later if left unused.

How Often Should You Do It?

Now, here’s another important question — how often do you need to shock your pool? If you cannot use your pool for eight hours after, surely you cannot shock your pool as often. The frequency with which you may need to shock your pool will differ from owner to owner. Depending on the climate you are in, the size of your pool, etc., you may need to shock it once a month or perhaps once every week. Either way, you need to be mindful that you don’t wait for a bacteria problem to worsen before you shock the water. If you feel your eyes or skin feeling irritated, you may have already allowed the problem to fester for too long.

So remember, the more frequently you shock the water, the greater the chance you kill any unwanted bacteria and algae before it has a chance to grow and reproduce. The few times when you should undoubtedly shock your pool are:

  • Before (and after) a pool party or any other instance of heavy use.
  • After a storm and especially if there are mud and debris in your pool the next day.
  • If there has been a change in water level.
  • If there has been any visible contamination, like any form of excreta (feces, urine) or bodily fluid (vomit) coming in contact with the water (it sounds unpleasant, but accidents can happen).

Final Thoughts

So there you have it — shocking your pool is not as scary as it sounds. As long as you take the adequate precautionary measures and are careful about proportions and your calculations, you should have no trouble shocking your pool. The first time may be a bit daunting, but once you get the rhythm of how the chemicals work, you can do it with your eyes closed (though I would prefer if you kept your eyes open when handling bags of chemicals!). So do what needs to be done and have a happy, healthy and clean swim!

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