What is Pool Shock?
Despite the scary name, shocking a pool has nothing to do with electricity. It does refer to a process of super chlorination by the addition of chlorine and non-chlorine chemicals that will raise the free chlorine level to destroy algae, bacteria and combined chlorine (known as chloramines). This in turn will provide a positive environment where other pool maintenance chemicals can work optimally.
Shocking your pool is best done when opening for the season, during and after a stretch of high heat, or after a busy pool party. It’s a vital task and when done in the proper sequence isn’t very problematic to complete.
What Are the Different Types of Pool Shock?
Since “shocking” a pool raises the free chlorine levels, many think that chlorine and pool shock are similar. While they may be in the same chemical category, they both have very defined roles in pool water chemistry.
Chlorine will help sanitize your water by attacking and killing bacteria and organic matter. This defense process creates chloramines, which can only be treated by shocking your water. There are several methods and treatments to make this happen.
Calcium Hypochlorite Pool Shock
Calcium hypochlorite (Cal hypo) is an inorganic compound that is water soluble. It is available as a granular solid or in liquid form to shock pool water. It contains about 65%-75% chlorine. There are two methods of adding Cal hypo to your pool water: in solid form, dissolving a pound in a five-gallon bucket, mixing and then pouring around the pool perimeter. The easiest way is with liquid pool shock, just remove the package cap and pour along the edge of the pool. Cal hypo is best applied at the end of the pool day or at night, as sunlight can destroy the unstabilized chlorine.
Dichlor Pool Shock
Sodium dichlor (dichlor) is a sodium-based pool shock that is in granular form. While dichlor can be used in chlorine pools, it is best used in saltwater pools or hot tubs and spas. There is no need to mix dichlor, just sprinkle along the pool edge. Dichlor will dissolve rapidly thanks to its sodium base, and the addition of Cyanuric acid will guard against the sun’s rays breaking down the chlorine too quickly. Dichlor can be used both as a shock treatment and part of regular pool upkeep.
Chlorine-Free Pool Shock
Chlorine-free pool shock uses Potassium peroxymonosulfate as its main oxidizer to remove non-living organic particles from your water. It is designed to be used in tandem with a water sanitizer like chlorine or bromine or with a saltwater generator. Chlorine-free shock can be used in pools and spas alike. It will not damage pool surfaces like other pool shocks possibly can and will improve your regular chlorine’s effectiveness. It is simple to use by scattering across the pool’s water surface, and water is swim ready in as little as 15 minutes. It should be noted that chlorine-free treatments will not kill germs or algae.
Granular Pool Shock
Granular pool shock and liquid pool shock both work to destroy foul-smelling chloramines as they clean and clarify pool water. Both have the same active chemical, but the potency and usage are different. Granular shock is fast dissolving, is available in larger quantities for maintaining a seasonal supply and can be stored for extended periods of time without losing potency. There are several different types of granular shock and multiple strengths. For these reasons, granular shock is the preferred shock treatment for many home pools.
How to Shock Your Pool
The objective of shocking a pool is to increase the level of free chlorine to approximately 10x the current combined level of chlorine. It is best to do your shock treatment at dusk or in the evening hours as direct sunlight will quickly burn off necessary free chlorine. If a daytime shock is done, make sure your treatment has a chlorine stabilizer such as Cyanuric acid to help preserve as much chlorine as possible.
Shocking Your Pool
When to Shock a Pool
Regularly adding chlorine to a pool helps maintain the proper level of free chlorine, but it may not generate enough free chlorine or increase the free chlorine levels quickly enough. Adding pool shock, also known as shocking a pool or hyperchlorination, helps to get rid of combined chlorine and generate free chlorine.
In general, you should shock your pool when you open it and close it. Throughout the season, you can shock it weekly or biweekly, but other factors may require more frequent shocking:
- You’ve had lots of people in the pool.
- There’s been a lot of rain.
- The weather has been very sunny.
- Temperatures have been high for several days.
- You see items like leaves, pollen, etc., in the water.
- You notice a strong chlorine odor.
- You notice large amounts of algae in the pool.
As with any pool chemical, read and follow all the instructions when using pool shock.
Need More Information?
If you would like more information on how to keep your pool in shape all season long, check out our DIY articles How to Maintain a Pool, How to Chlorinate a Pool and Why Is My Pool Water Green? How to Get Rid of Pool Algae.
Frequently Asked Questions
Here are some answers to frequently asked question on how to shock a pool.
What time of day is best to shock a pool?
It is preferable to do a pool shock in the late evening or after dark to avoid the sun's UVA and UVB rays from reducing the amount of free chlorine available. For daytime shocks, use one that has a chlorine stabilizer to help preserve the chlorine.
Can you over shock a pool?
It is possible to over shock a pool by adding too much shock treatment and having an overabundance of chlorine. You can let the sun's rays burn off the excess chlorine in about 48 hours. Do not use the pool until chlorine is 3 ppm or less.
How often should you add shock to a pool?
Adding shock should be a part of your weekly pool maintenance program. A pool that gets daily use should be shocked once a week. Pools with less activity can go to an every other week schedule.
Can you shock a pool two days in a row?
Yes, and if algae is the main problem then a consecutive shock treatment is recommended. Also a double shock is suggested after prolonged rain or heavy daily use.
How long do you have to wait to swim after you shock a pool?
It is recommended to wait at least 8 to 24 hours after shocking your pool to resume swimming. The key is to check the free chlorine level and make sure it is 3 ppm or lower.
How much shock do I need for a 1,000 gallon pool?
A general rule is 1 pound of pool shock for every 10,000 gallons of pool water. Using that reference, you should use 1.6 ounces of pool shock in a pool that has 1,000 gallons of water.
How long does it take for a pool to clear up after shocking?
Depending on your pool size and filtration system, it can take up to 24 hours for your pool water to return to its correct balance. When the chlorine level is below 4 pmm and the pH balance is 7.4-7.6, it is safe to enjoy swimming again.
Can you shock a pool during the day?
The most beneficial time to shock your pool is late evening after the sun has set. The daytime UV rays of the sun will dissolve the chlorine. If this isn't doable and you must shock during the day, make sure you pool shock has a chlorine stabilizer like Cyanuric acid which will help protect the chlorine from losing its efficiency.
Do I need to shock a saltwater pool?
While saltwater pools do generate their own chlorine, it is advisable to shock the pool water regularly to keep it clean and safe. Use a dichlor shock or a non-chlorine shock for saltwater pools.
Will shocking a pool kill mosquito larvae?
Chlorine by itself will not kill the mosquito larvae, but it does make a less inviting environment to lay their eggs. Copper sulfate, an algaecide, will help eradicate the larvae. Also, keep your pool clear of leaves and debris, as mosquitoes like to lay eggs in dirty pool water.