Shocking a pool is a routine process that every pool requires at least once a year. We suggest every pool owner learn what it means to ‘shock a pool’ and how to do it.
Shocking a pool helps to eliminate algae by rapidly raising the chlorine level of your pool water. The procedure is called “shocking” because it involves introducing a measured amount of concentrated chlorine liquid or powder into the pool that will immediately commence killing algae and bacteria. This induces as an immediate “shock”, as opposed to regular chlorine tablets which gradually dissolve and disintegrate over time.
Shocking a pool is one of the easier maintenance procedures that can be done to keep your pool clean, so learn all about it in this article so you can add it to your pool maintenance procedures.
What is ‘pool shock’?
Pool shock is a chemical that oxidizes chloramines in your pool’s water. “Shocking” your pool is a more commonly used term for superchlorination. Chloramines develop when chlorine mixes with naturally occurring nitrogen in sweat, oils and urine. This is nothing to be concerned with, as it is a natural chemical process and byproduct of chlorine doing its job effectively. If your pool is appearing cloudy or slightly green, then algae could be growing, and shocking your pool could be a good idea.
Before you begin
Before shocking your pool, ensure you inspect the overall condition of your pool’s plumbing for leaks or blockages. A leak at any time can cause chemicals to escape, causing corrosion and posing a health risk. Leakage always need to be repaired when detected and when your system is again watertight, it is safe to shock your pool.
Always take safety precautions
Pool shock is concentrated chlorine in either powder or liquid form that begins to dissolve immediately upon contact. Just like chlorine used for regular pool maintenance, pool shock is likely to bleach clothing and burn or irritate your skin and eyes.
Always read the safety precautions before handling chlorine shock or any other chemicals. Familiarise yourself with what to do in case of an emergency and be prepared for anything. Keep clean water within reach in case the chlorine does make contact with your skin or eyes.
Chlorine is a dangerous chemical so always handle it with extreme care and store it safely and securely. Here are a few tips to remember:
- Never add shock through your pool skimmer, especially if you have an automatic chlorinator
When the shock treatment mixes with the chlorine, it causes a dangerous gas, which can lead to your chlorinator exploding! Gently pour the shock into the water. - Always wear protective gear, especially goggles and chemical-resistant gloves, when handling chlorine
Pool shock, especially calcium hypochlorite, can release small amounts of chlorine gas, adding to the danger of chlorine making contact with your skin and eyes. Wearing protective gear can reduce the likelihood of exposure and potential contact. - Avoid directly breathing chlorine gases
Exposure to chlorine gas potentially causes throat and lung irritation. Handle chlorine products in a well ventilated space, or outside in the open, and avoid breathing to close to any containers used in the pool shock process. Wearing a chemical mask is a great idea for additional protection. - Never mix different types of pool shock chemicals
Mixing different types of liquid chlorine or mixing liquid and powdered chlorine together can cause a volatile, unexpected and dangerous reaction. Add each chemical to your pool separately. Only use one open container of a chemical at a time to avoid mixing old and new chemicals together. - Follow product instructions
Some pool shock chemicals require pre-dissolving with water before being added to the pool. Do not add pool shock directly to the pool water unless the instructions advise it is safe to do so.
Types of Pool Shock
Regular chlorine tablets are designed for gradual release and therefore won’t work effectively to shock to your pool. We recommend speaking with your local pool maintenance specialist to discuss the best type of pool shock for you.
Calcium hypochlorite
Used to disinfect swimming pools and municipal water sources since 1928 calcium hypochlorite is one of the most common and inexpensive products to shock your pool.
Lithium hypochlorite
For pool water with high calcium content, lithium hypochlorite could be useful. It dissolves quicker than calcium hypochlorite and can be added directly to your pool without pre-dissolving beingnecessary.
Dichlor
Dichlor can also be added directly to your pool and is also appropriate for shocking saltwater pools.
Non-chlorine shock
Another preferred treatment to shock a saltwater pool, non-chlorine shocks that use potassium peroxymonosulfate act quickly and are inexpensive.
How to shock a pool – the process
1. Familiarise yourself with shock
Every manufacturer’s chlorine shock varies slightly so always read the packaging and instructions thoroughly, and seek professional advice with any queries. Follow the product instructions as prescribed – no improvising.
2. Test the pool water quality
Do a quick round of pool water testing. The Free Chlorine level should be lower than the Total Chlorine level. This means your Combined Chlorine level is off and it’s time to shock your pool.
Also, check the pH and alkalinity levels. Make sure your pH level is between 7.4 – 7.6 and your alkalinity level is between 100 and 150 parts per million (ppm). This will balance the pool water chemistry so the shock treatment is more effective.
You can also check your calcium hardness level to make sure it’s in balance with the pH and Alkalinity. If your pool has a vinyl or fiberglass liner, the calcium hardness level should be between 175 parts per million (ppm) and 225 ppm. If you have a concrete or plaster pool, keep the level between 200 ppm and 275 ppm.
3. Prepare the pool shock
Once you have all the necessary equipment and chemicals nearby, turn on your pool’s pump and ensure it is filtering normally. Carefully read the pool shock’s usage instructions. Most products’ packaging includes a chart or steps to help calculate the quantity of shock you need.
If you need to dissolve the shock first, fill your bucket roughly ¾ full with warm water. Add the shock to the bucket, and slowly stir until the chemical is as dissolved as possible. Work in one-pound increments.
If you do not need to dissolve your shock, count how many containers of shock you need. Add one bag at a time until you reach your calculated break point.
4. Add the pool shock to the water
At this point, make sure your pool pump and pool filter are running at full speed. This will help mix in the shock more effectively. Keep the system running for at least 8-12 hours after adding shock.
Slowly pour the shock while walking around your pool for more even distribution. (If your shock-water mix has solid particles at the bottom, dip the bucket into your pool water, carefully swish around to dissolve, and keep pouring.)
Shock should be added front of the return fitting and around the edge of the pool to make sure that it mixes properly and doesn’t concentrate in one area and bleach your pool finish. While adding the chlorine shock, be sure to make it around the pool at least one time to help distribute the shock. Do not add all the shock in one place as it will bleach your vinyl liner or whatever pool finish you have.
5. Brush the pool
Brushing the pool after adding shock helps eliminate the risk of bleaching your pool while simultaneously loosening up whatever algae is on your pool’s finish (if your pool walls or floor are slippery, that is algae). It is very important to brush the entirety of your pool including the walls, paying careful attention to the water line. If the water line is not scrubbed with the brush, there is a good chance that the line will become permanent.
The best practice is to brush the entire pool walls and floor first, even if it is above the water line, pushing everything towards your skimmer mouth in a continuous motion. Then go back around again and brush the water line. Be as rough as you can with the water while doing this, the idea being to disturb as much of the debris and water as possible so as to dislodge the algae so it floats on top of the water and the filter can pick it up.
If the pool gets cloudy while brushing the pool, that’s actually a good thing. It’s a sign that you are loosening up what is causing the problem, and the pool should return to a clear pool within a few days.
6. Run the pump and filter
Now that the pool has been shocked and brushed down, the algae and debris will be floating at the surface. Leave your pump running on (this includes overnight) until the water becomes clear. It is perfectly normal for it to take a few days (usually 2 to 3 days) of continuous running to allow the filter to remove all of the algae and whatever else was in the pool.
While the pool is running during these few days, it can be helpful to brush your pool daily to pick up what has settled back on the floor.
Be sure to keep an eye on the filter pressure while leaving the pool on. If you notice the PSI is higher than normal, backwash your filters and empty the skimmers baskets for the pool and your pool motor.
Wait to use your pool based on when you added the shock and the manufacturer’s recommendations. You don’t want to irritate your skin and eyes or bleach your swimsuit.
How to shock a saltwater pool
Is it okay to shock a saltwater pool? A lot of pool owners think saltwater pools are different from traditional chlorine pools. But the salt in the water passes through a generator which turns it into chlorine. All saltwater pools are actually chlorine pools. Check out our post “Saltwater pools – everything you need to know“. One benefit is that chlorine doesn’t need to be regularly added to the pool – it is generated and recycled by the saltwater system.
This means you can shock your pool using the traditional shock methods outlined in this article. However, it is recommend to only use Dichlor or non-chlorine shock for saltwater pools.
Most saltwater generators do however include a “super chlorinate” button that increases the chlorine production so a full shock may not be necessary.
It is suggested to do this once every week or two, depending on weather conditions and pool usage. After heavy rain or high usage, shock your saltwater pool once a week.
How to shock a pool FAQ
Are chlorine and pool shock the same thing?
No. There are variants of pool shock that have chlorine in them, like calcium hypochlorite. There are also pool shock products that have no chlorine in them.
Can I shock my pool without the pump running?
It is recommend to run your pump and filter when you’re actively shocking your pool and to keep them running for around 8-12 hours afterward. You may run the risk of bleaching your pool’s floor, walls and surfaces by not circulating the chlorinated water with the pump and filter running.
How long should I wait to swim after shocking the pool?
It’s usually safe to swim after letting the shock circulate in the water for at least 8 hours. Test the water’s chlorine levels though before jumping in, as they may still be elevated and therefore dangerous for swimmers.
Does pool shock work in cold water?
Cold water is not a problem, though if the pool shock requires dissolving before being added to the pool, use warm water to help this process. This will help the shock dissolve more effectively so it won’t sit on the bottom of your pool and cause bleaching. It also helps the mixing process with the pool’s water.
Is it a different process for above-ground pools?
The process for shocking an above-ground pool is the same as an in-ground pool. If your pool has a main drain then while brushing your pool down, brush towards the main drain.
When to call in a professional
If after a few days your pool is not clearing up, is still visibly cloudy or green, or has elevated chlorine levels, then it’s time to call in a professional.
Some strains of algae are known to be particularly stubborn and can require more specialised algaecides to eliminate. A professional can also detect and diagnose what may be causing excessive algae, whether it is a treatment issue or a mechanical one, such as a failing pump or filter.
Searching for a local pool cleaner or maintenance professional? Try finding one in our directory, along with local pool supplies to grab what you need to shock your pool.
Summary
Shocking a pool is one of the easier maintenance procedures that can be done to keep your pool clean and safe, so brush up on the basics or seek professional help.
