When I first got a pool, I thought it would just be cleaning it with pool tools and adding the right amount of chlorine. But I was surprised that there were more processes that need to be done. You need to test the water chemistry, add special chemicals to balance the water, and shock the pool.
The last one was more complicated for me, but it’s a process that both new and old pool owners should know about. It was intimidating at first, but once I knew why it’s important and how to do it, it became easier.
To help you out with your journey to keeping your pool pristine and algae-free, here’s what I learned about pool shocking.
What is Pool Shocking?
You may think that adding chlorine is enough to keep your pool clean. That’s why when there’s a chemical smell, it feels as if the pool is getting cleaner. But that smell doesn’t mean it’s getting cleaned or caused by just the chlorine, it’s actually because of chloramines.
Chloramine is a mix of chlorine and nitrogen from body sweat, oil, or urine. We can’t prevent them from mixing because it’s part of the cleaning process. Unfortunately, it brings odor and may cause eye and skin irritation. Aside from the smell, signs of chloramine warn us that the pool water is not treated properly. So this is where pool shocking comes in.
Pool shocking or (super)chlorination is the process of adding the right amount of chlorine to destroy the chloramines or combined chlorine (to be discussed in the next section), pathogens, algae, and other organic matter. The term pool shock refers to granular oxidizer or powder chlorine, so adding a granular oxidizer means shocking a pool.
Is Pool Shock different from Chlorine?
Before we discuss if a pool shock is similar or different to chlorine, let us first understand what chlorine means.
The term ‘chlorine’ has been used to describe the most common sanitizer in the world and sometimes it is used wrongly. If we talk about real chlorine, this one is in gas form. The one we use in pools is hypochlorous acid, which is derived from real chlorine and mixed with other chemicals to make it liquid or solid.
To answer this question, pool shock is chlorine but they are also different because of their purpose. A pool shock is chlorine in high dosage which is used to quickly increase the chlorine levels of the pool while chlorine is used to maintain the chlorine level. It is important to use both because, without the pool shock, the pool will not reach the chlorine level to fully sanitize. If you don’t use chlorine, the pool shock will dissipate immediately.
We should also discuss what free chlorine, combined chlorine, total chlorine, and breakpoint chlorination means. Free chlorine or FC is the current chlorine level disinfecting your pool water. It is recommended to keep the FC level between 1 to 3 parts per million for the chlorine to be effective. On the other hand, combined chlorine or CC is the used chlorine. It’s still present in the pool but isn’t actively sanitizing anymore. The goal is to keep the CC levels less than 0.2 parts per million. The sum of FC and CC is simply the Total Chlorine or TC.
Use water testing kits to measure the TC and FC of your pool water. Then compute for the CC with this formula: TC - FC = CC.
Breakpoint chlorination is when you have the right FC level to remove chloramine buildup. To reach this point, you need to add ten times the CC level by using a pool shock. So the goal of shocking your pool is to reach the breakpoint chlorination. If you don’t, find out in the next section.
Why should you Shock your Pool?
If you don’t shock your pool, the chloramines may increase in your pool water and if this level continues to rise, you would have to replace a part or all of your pool water. Having more chloramines will also make your pool water cloudy.
Aside from removing the chloramines or CC, shocking your pool also destroys or oxidizes bacteria (harmless or pathogenic), algae, and other contaminants present in the pool. This process will also purify and disinfect your water and help you avoid clearing cloudy water. You may not need to consistently remove algae as it can treat budding algae in crevices and corners.
Pool shocking will also help keep the FC active and properly balanced with Cyanuric Acid. If the Cyanuric Acid is higher, this will make the FC ineffective. Here is a CYA / Chlorine Chart so you know how much chlorine to add based on the Cyanuric Acid level.
As a bonus, it can also help remove organic stains on the pool surface. This can also be used to sanitize your pool when you’re having trouble with the filter, pump, or salt system.
How to Shock your Pool
What you will need:
- Pool shock (1 pound)*
- Bucket (5-gallon size)
- Stirring stick
- Eye protection
- Gloves
- Water test strips
*For a 10,000 gallon pool, you will need to use 1 pound of pool shock. Buy more depending on your pool volume.
If you don’t know your pool volume, you can use this pool volume calculator to know how many gallons your pool is.
Step 1. Test the water
Make sure that the pH level is between 7.2 - 7.6. If it’s not, adjust it first before shocking your pool.
Step 2. Safety first
Wear eye protection and gloves before starting the process. You should also wear old clothes since this chemical contains a high concentration of chlorine that can bleach them.
Always check the label and follow the instructions written on the pool shock packaging.
Note: Do not add or dissolve other chemicals into the pool water before shocking the pool.
Step 3. Mix the pool shock and water
Get a bucket and mix the water and pool shock. The ratio is 5 gallons of water to 1 pound of pool shock. Carefully mix the solution.
Note: Always put the water first before the pool shock.
Step 4. Spread the Pool Shock-Water mixture
Before spreading, you should make sure that the pump and filter are running or the pool is on. When it is, spread the mixture all over the pool. Let it run for eight hours or overnight.
Alternatively, there are also pool shock brands where you can directly spread it. Apply it at the deepest part of the pool and then use a brush to disperse the powder that has settled at the bottom.
Note: If you have vinyl liner or pool, use the bucket or pre-dissolved pool shock method.
When and how often should you do Pool Shocking?
Aside from removing chloramines and the presence of algae, here are other times you should shock your pool:
Before and after the swimming season: When opening your pool after a long break or closing it for a few months, you need to shock your pool after balancing the water chemistry. This way, it will be safe to swim in and help clear the water. You should also do it when closing the pool to disinfect the water.
After a heavy rainfall: When rain falls into the pool water, it also drags dust, pollen, air pollution, and algae spores that can cause water discoloration, increase chloramines, and change water chemistry. This isn’t always necessary but it is recommended to do this just to be on the safe side.
After a swimming party: The day after a successful swimming party, you will need to shock it because it probably has been contaminated with organic matter such as body oil, urine, feces, or vomit. This doesn't necessarily mean that it is visible to the eye - it can be tiny particles floating in your pool water.
Continuous sunny weather: When the sun is out, it means the chlorine levels will go down because of the hot temperature. If the water temperature increases to more than 88°F, you will need to shock your pool.
Since the sun weakens the chlorine. It’s important to…
ALWAYS shock your pool during dusk or evening. This will help make it more effective and keep the free chlorine at the right level.
Now that you know when to do it, how often should you shock your pool?
It is recommended to shock your pool once or twice a month and then every week during the summer. But every pool is different. Pool shocking frequency depends on the climate, location, pool cleaning system, and pool usage. You may think your pool is clean since it is clear, but the only way to make sure it is sanitary is by shocking it.
So if you’re not sure if you should shock your pool, check the first paragraph of this section. This tells you when you should do pool shocking.
Shocking your pool regularly will also help prevent bacteria and algae from settling in your water. This will also eradicate the smell that these contaminants bring.
Recommended Pool Shocks
Pros
Cons
Pros
Cons
Pool Shocking: Frequently Asked Questions
Let's get your questions answered!
How long should you wait after Pool Shocking?
This is by far the most common question on pool shocking.
It’s not how long, but what FC level is safe for swimming. You can go into the pool when the FC level is between 1 to 4 parts per million. Some wait a day before swimming in a newly-shocked pool just to be safe. You can also check the manufacturer’s instructions regarding the wait time.
What happens when you Over Shock your Pool?
For the chlorine levels, don’t worry because it will burn off after 2 days. You should be more worried about under-shocking it. Make sure to check the manufacturer’s instructions, water chemistry, chlorine levels, and follow the steps to properly shock your pool.
How and where do you store the Pool Shock?
For your pool shock, make sure to store it in a cool and dry place. If you store it in a location with high temperature and humidity levels, this will solidify the pool shock. You should also place it in a tight-lid container to prevent off-gassing and contaminations.
Is it fine to Shock a Saltwater Pool?
If you have a saltwater pool - lucky you! It is more low-maintenance than a chlorine-based pool. But if there is an algae build-up or other contaminants in the saltwater pool, then you might need to shock your pool. Here’s a guide on how to do saltwater pool shocking.