Shocking the pool is a key part of running a clean (and usable!) swim pool. Here’s a detailed look at signs you need to shock the pool, how often do it, and steps for doing it like a pro. Clean pool water, engage!
If you’re a new pool owner, you may have heard the term “shocking your pool”.
While it sounds like a bit of a scary term—and no, we aren’t going to run an electric charge through the water—it’s actually fairly straightforward.
Shocking the pool involves using chlorine or other sanitizers to temporarily increase the amount of chlorine, in turn zapping pesky bacteria, algae, breaking apart combined chlorine (which is “used” chlorine), and otherwise sanitizing the water.
Shocking the pool is one of the most effective ways to bring your pool chemicals back into balance and keep your pool nice and sparkling clean.
It’s also something you should do regularly to stay ahead of bacteria and algae buildup.
If you’re confused about when and how you should shock your pool, we have you all taken care of.
In this guide, we’ll cover the usual suspects (symptoms) for when it’s time to shock the pool, how to do it properly, and answer some of your most shocking (ha!) pool shock questions.
Let’s jump in!
Signs You Need to Shock Your Pool
You peel back the cover of your above-ground pool, drink in hand, ready to enjoy the pool–and, boom.
Cloudy, greenish, yucky pool water.
In this instance, you know that shocking the pool is in your future.
But there are other less obvious situations where you are going to want to reach for the shock.
When Opening the Pool
After your pool has been covered for an extended chunk of time or an entire season, and it’s time to open the pool, you should shock your pool.
No matter how well you winterize your above-ground pool, there’s almost guaranteed to be some excess bacteria, cloudy water, and any other unwanted pool guests.
Shocking the water will help get rid of a large part of these unwanted microorganisms and get you on your way to clean, swimmable water again.
After Heavy Use
Fun fact: people are kinda dirty! The sunscreen, the sweat, the pee, the hair—all of that stuff sheds into the water and eats up free chlorine.
Increased use of the pool means a commensurate increase in bacteria and other contaminants left behind after the last swimmer has toweled off and gone home.
See also: How to Clear Cloudy Pool Water
You’ll likely notice the pool water is a little cloudier than usual after a lot of people have been in and out of the water.
Shocking the pool will increase chlorine levels after heavy use and help sanitize.
After Hot Weather or Heavy Rain
When it’s been hot for quite a while, it can cause your pool to also raise in temperature.
Higher temperatures can trigger the growth of bacteria and decrease chlorine efficacy.
Heavy rains can also cause contamination of pool water, increasing pH.
Either way, a shock can help restore balance.
Strong Chlorine Smell or Irritated Eyes/Skin
Contrary to what public pools and conventional wisdom will tell you, the smell of really strong chlorine is actually a sign that there’s an increased amount of combined chlorine in your pool.
(Combined chlorine, also known as chloramines, is the byproduct of free chlorine and organic matter coming together and making a smelly lovechild.)
Combined chlorine is what also causes itchy, red eyes and skin.
A pool shock can get rid of that combined chlorine/chloramines while offering higher free chlorine levels.
Serious Algae Growth
If you notice algae growing in your pool, the best way to combat it is by significantly boosting chlorine levels.
Keep in mind that using pool algaecides is also an excellent way to prevent excess algae growth in the first place, but a good pool shock has a role to play here, too.
Shocking Your Pool Like a Pool Pro
Before we jump in and start shocking away, it’s important to get a grasp of the basics of what we are shocking the pool with.
1. Determine the Right Amount of the Right Kind of Chlorine
First, let’s talk about the different types of chlorine.
- Free Chlorine (FC): The amount of chlorine in your pool actively working to sanitize the water. These levels should be between 1 and 3 ppm.
- Combined Chlorine (CC): This refers to the chlorine that’s already been “utilized.” Yes, it’s in the pool water, but it doesn’t quite sanitize effectively. These levels should be less than 0.2 ppm.
- Total Chlorine (TC) is the total sum of FC and CC together.
- Breakpoint Chlorination (BC): This is when the FC is high enough to break molecular bonds of chloramine.
When you reach BC, the free chlorine will start to build up.
When shocking a pool, we want that free chlorine to be around 10 times the combined chlorine level, achieving breakpoint chlorination.
2. Test Pool Water
One of the things you will get insanely good at being a pool owner is testing and retesting the water.
When shocking the pool, you should test before throwing anything in so that you have a baseline of how much shock to put in.
At this point, pre-shock, the free chlorine level should be lower than the total chlorine level.
What this signifies is that your combined chlorine level isn’t balanced, and needs a shock to regain it.
While you got your handy little pool test strip or digital pool test kit out, may as well check everything else, too!
You also need to be revising pH and alkalinity, as all are incredibly important and affect one another.
pH should be within 7.4 and 7.6, while your alkalinity should be between 100 and 150 ppm.
By ensuring your pH and alkalinity levels are within these ranges, you’re creating the perfect water chemistry to maximize shock treatment efficacy.
3. Check Calcium Hardness
Does your pool come with a vinyl or fiberglass liner, like most above-ground pools?
Then calcium hardness should be between 175 and 225 ppm.
If yours is made with concrete or plaster instead, raise that level to between 200 and 275 ppm.
4. Pre-Dissolve Pool Shock
Whichever pool shock you settle on, it’s always recommended that you read the instructions it comes with and shock accordingly.
Most reputable products will come with some kind of chart or step-by-step instructions so you can accurately calculate how much you need.
There’s really not a whole lot of guesswork involved, and after the first couple of times, you should be able to apply it correctly without even needing to refer to the instructions.
Many products will indicate for you to first dissolve the shock in a separate container outside of the pool.
You’ll do that by taking a bucket with about ¾ full of warm water, gently adding the shock to the bucket, and slowly mixing until dissolved.
5. Add Pool Shock to Pool Water
There are many pool shocks that do not require you to pre-dissolve them.
If that’s the case with the one you’ve chosen, first determine how many containers of shock you need.
We highly recommend taking it slow and adding just a bag/container at a time until you have added the right amount.
As you pour, walk around the perimeter of the pool to help evenly distribute it.
Your pool pump and filter should be operating at full speed for around 10 hours to help better mix in the shock.
And remember to keep the pump and filter running so that water circulates and you don’t bleach the sides of your pool.
6. Shock the pool overnight
Finally, there is a best time to shock your pool, and that’s once the sun goes down.
Start your shock at dusk, so that it processes throughout the night.
Doing so in the daytime will result in the sunlight burning off chlorine, yielding the shock ineffective.
I know we’ve hammered ya with a lot of chlorine talk, but it’s important to remember the difference between stabilized and unstabilized chlorine.
Stabilized chlorine has cyanuric acid (a stabilizer, hence the name) added to it which keeps the chlorine from rapidly degrading from UV exposure.
Unstabilized chlorine is less expensive, but left exposed to the sun will burn off and you’ll watch the cost savings (and your pool chemistry) go up in smoke.
How to Shock the Pool Safely
Because safety never takes a holiday, you know?
Beyond not pumping pool shock through your automatic chlorinators—which will damage both the skimmer and accumulate some potentially dangerous gases—here are a couple more best practices for applying pool shock safely and efficiently:
1. Avoid Breathing from Containers and Use Gloves
We are talking about pool chemistry and chemicals after all!
Try to face away from the container when breathing in.
It’s even better if you can grab a chemical mask to wear as you’re mixing and pouring the shock.
Breathing in chlorine gas is not a good idea, and can easily cause throat, nose, and lung irritation.
Handle pool chemicals with gloves to reduce skin irritation, as well.
2. Never Mix Pool Shocks
Even if it’s the same brand, just don’t do it unless you want to turn into some kind of Ninja Turtle.
By mixing pool shocks, you could potentially end up creating toxic gases that could even be deadly.
Even mixing liquid chlorine or dry chlorine granules can create volatile chemical reactions.
Again, just follow the instructions on your pool shock, and you’ll do just fine.
Shocking the Pool – FAQs
Can you shock a pool too much?
Yes, you can shock a pool too much.
If the free chlorine levels are over 5ppm, the water is not safe to swim in. Remember, 1-3ppm is the sweet spot where we want free chlorine to hang out.
If free chlorine is higher than recommended, take the cover off the pool and let the sun hit the water, it will burn off and degrade some of the free chlorine.
Secondly, remove any floating chlorine dispensers that are still pumping product out into the water until the pool chemistry is in balance again.
Can you swim right after shocking the pool?
You should wait at least a full 24 hours or until chlorine levels reach levels of at least 1ppm and no more than 4-5ppm and pH levels are in the range of 7.2 to 7.8.
Chlorine, as amazing of a disinfectant as it is, takes time to circulate through your pool and sanitize the water completely. Monitoring pH will also tell you how ready the pool is for action again.
Can you shock a pool every day?
While the frequency at which you shock your pool depends on various factors (use, environment and weather, etc.), you probably don’t want to shock it every day because you would never be able to use it.
After all, you won’t be able to use your pool until a minimum of 24 hours have passed after you apply the shock.
Outside of the “hot and heavy” special occasions that warrant a special shock, you should only really have to shock the water every two weeks or so with regular use.
Even if you’re using your pool on a daily basis, the recommended shock frequency is every 2 weeks or so.
Shocking the Pool – Wrapping it Up
In order to achieve a clean pool so that you can get the most of it this summer, shocking it regularly and properly is crucial.
But, once you get a hang of testing and shocking the water, you will be able to rest easy, knowing that your pool water is going to be ready for those hot summer afternoons.
Now that you’ve got the grasp of how to shock the pool like a champion, get to it and enjoy that sparkling blue water!
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