How To Choose The Right Type Of Swimming Pool Shock


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There are several types of swimming pool shock available on the market. You may find yourself asking "what's the difference" or "which one should I use". Reading this guide will help you determine which is the best type of shock for you.

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Step by Step


Step 1

What's the difference?- There are 3 main types of pool shock available on the market. They are: calcium hypochlorite (cal-hypo), sodium di-chlor (di-chlor), and potassium monopersulfate (non-chlorine/oxidizer).

Step 2

Cal-hypo is the most popular shock used as well as the strongest shock available. Cal-hypo is a quick dissolving, unstabilized shock which means that the sun's uv rays will burn it off quickly and it will not increase the cyanuric acid level in the swimming pool. It is quick dissolving but should be pre-dissolved before adding it to the pool. Failure to do so may cause pinholes in a vinyl liner and/or bleaching of the pool surface. Cal-hypo shock purchased in a "big box store" will be weaker compared to the same product purchased from a swimming pool supplier (Inyo Pools). This is because a "big box store" has restrictions as to the type of chemicals they can carry. Cal-hypo shock will usually raise the pH level when added to the swimming pool. Cal-hypo should be added in the evening and swimming can be resumed once the chlorine has returned to normal levels.

Click Here to View our Cal-Hypo Pool Shock 


Step 3

Sodium di-chlor is a slow dissolving, granular chlorine that is stabilized. It will last in the water longer than cal-hypo would. Di-chlor contains stabilizer which will increase the cyanuric acid level in the swimming pool. It can be used as a shock treatment (1 lb per 10,000 gallons) or as a maintenance chlorine (3 oz. per 10,000 gallons). Sodium di-chlor will usually raise the pH level when added to the swimming pool. Di-chlor should be added in the evening and swimming can be resumed once the chlorine has returned to normal levels.

Step 4

Potassium monopersulfate is an oxygen based shock and contains no chlorine. Non-chlorine shock is primarily used to oxidize the water and remove contaminants from your swimming pool. It actually helps the chlorine work better. This type of shock is commonly referred to as "shock and swim" because it can be added at anytime during the day. Swimming can be resumed 15 minutes after the product is added to the swimming pool. Non-chlorine shock will not affect the cyanuric acid in the swimming pool.

Click Here to View our Non-Chlorine Shock 

Step 5

Which one should I use? The type of shock you should use will depend on the water chemistry and why you are shocking. If the water is green, I would recommend using the cal-hypo shock. If you are shocking as part of a weekly maintenance and the pool looks clean, you can use either of the 3 shocks. I normally would recommend the non-chlorine shock be used every other week (week 1 chlorine shock, week 2 non-chlorine shock, week 3 chlorine shock etc.) or before or after a heavy bather load. I would also recommend using a non-chlorine shock if bromine is used as the primary sanitizer. 


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 Posted: 12/5/2021 

Hello, We have a vinyl liner salt water pool with a Hayward salt generator. The pool water looks great however, the chlorine levels test very high. We put the cover on mid-November when the weather cooled off and turned the salt generator off. We've been having some really warm and dry weather so we pulled the cover off and also added water to the pool, in the hopes that this would reduce the chlorine levels. It has not. We are done swimming for the season but regardless it seems we should get our chlorine levels down. On a test strip Total Chlorine is easily a 10 and Free Chlorine a 5. Any suggestions would be appreciated.

InyoPools Product Specialist  Posted: 12/8/2021 

There are two things you can do: wait for the chlorine to dissipate naturally or drain a portion of your water and refill with fresh. 

 Posted: 7/14/2020 

chlorine levels are always high how can I bring them down

InyoPools Product Specialist  Posted: 8/25/2020 

Stop adding chlorine and the chlorine level will naturally come down. if you are dosing the pool based on a set schedule without testing, i suggest introducting a test strip test into your routine. The only reason chlorine is high is because you are adding. Start testing the water, and only add chlorine when necessary.

Anonymous  Posted: 7/8/2020 

Can I use shock made for a salt system with a sand filter?

InyoPools Product Specialist  Posted: 9/23/2020 

Yes, you can. Sand filters can be used on traditional chlorine or saltwater systems.

 Posted: 7/15/2019 

If you rotate a chlorine based shock with a non-chlorine based shock (e.g., every other week as recommended), how do you test for the chlorine in the pool with a test kit, or is there another method to test the water? Thanks - great site and service.

InyoPools Product Specialist  Posted: 7/16/2019 

The way you test the chlorine levels wouldn't change; use test strips or a Taylor testing kit.

 Posted: 6/29/2019 

I have hard water and it’s a bit green. My ph won’t come down but everything else is good.what do I do

InyoPools Product Specialist  Posted: 7/3/2019 

Add calcium decreaser/hardness decreaser to soften the water. Second, add muriatic acid to the water to lower the pH. Once the pH is in check, then add your chlorine to make sure you maximize its effectiveness.

 Posted: 6/17/2019 

What type of shock is best to use in a salt water pool with a pentair IC40 generator? Is there any that are harmful to the cell?

InyoPools Product Specialist  Posted: 6/20/2019 

You may use any type of shock options in a salt pool including liquid chlorine. 

 Posted: 5/23/2019 

Hi, I have a 18x36 above ground pool, I am in the process of clearing it of light green water. I have been using a calhypo shock. All of my chemical readings are good except my chlorine is low. I have 2bags of sodium dichlor on hand,,can I mix the two,? Txs

InyoPools Product Specialist  Posted: 5/23/2019 

Hello Barbara - We wouldn't recommend mixing the dichlor and cal-hypo in the same bucket. However, you could add dichlor to a pool after it's been shocked with cal-hypo.

 Posted: 4/28/2019 

Thank you this is very helpful. So when would I use liquid shock? Would I use that just during the week if the chlorine level goes down?

InyoPools Product Specialist  Posted: 4/30/2019 

Hello Tara - The liquid shock can be used any time. Most people use tablets to maintain a chlorine level and shock the pool once a week with liquid shock  Others use liquid shock daily to maintain a chlorine level.

 Posted: 9/8/2019 

Liquid Chlorine say 10% (HASA Chlorine I use) is the #1 sanitizer for pools used to keep pool water safe to swim in which requires regular maintenance of daily amounts enough to keep the ppm where they should be for your pool and given how much CYA ppm exist in the pool at the time. If you use liquid Chlorine and not "pucks" then you probably keep a consistent CYA level as recommended to help stabilize the chlorine from rapid burn off from the sun UV. Should your pool not maintain enough FC, you can begin to see yellow film forming on the walls and steps mainly in shaded areas of the pool. If you take action right away and consistently with first brushing and then "Super Chlorinating" with the same liquid chlorine but at a much higher dose and continue this for several days, it should be gone. Liquid chlorine has a component of salt because it's Sodium Hypochlorite so it will had some salt to your pool but it takes a whole lot before it's a concern. You can use Cal Hypo to shock but consider the Cal stands for Calcium which is in high concentration in shock and a mineral that you may not want to add to your plaster pool/equipment. Another shock is a Di-Chlor shock and the down side to using this one is it is has the CYA component. To much of that in your pool and your chlorine sanitizer becomes less effective, therefore it increases your chances of getting algae or you have to increase your maintenance of Chlorine, but too much CYA can lead to Chlorine lock and usually the only recourse is removing the CYA by draining or filtering the water. So that one gets expensive and why I don't use it to sanitize even for maintenance. Cleaning filters or backwashing along with brushes used is recommend and . I try not to add a lot of chemicals to my pool water because of the exposure to the human body through skin absorption when you swim so I want to keep the ppm of Chlorine and or other chemicals to a heathy limit.

 Posted: 3/21/2019 

Hi I’ve added this to my hot tub, and noticed I’m getting high chlorine readings. Previous shock I’ve used don’t do this.... can you explain why this is. Thanks

InyoPools Product Specialist  Posted: 3/21/2019 

What are you referring to when you say "this"? If you are adding chlorine shock but was using non-chlor shock before, then that is where you difference is.

 Posted: 3/3/2019 

I have an indoor endless pool where NO sunlight can reach. I am told not to use stabalised chlorine. Can I use a small amount of shock chlorine each day to maintain minimum chlorine levels? Do I have to shock the pool each week if i am only using shock chlorine daily. I also have a nature 2 cartridge fitted

InyoPools Product Specialist  Posted: 3/4/2019 

Yes, you can use a small amount of liquid shock each day to maintain a minimum chlorine level. You would not need to shock the pool weekly.

 Posted: 4/14/2020 

How often should I shock a 1013 gallon indoor pool that gets no sunlight? Would a non-chlorine shock be best since I lose chlorine very slowly?

InyoPools Product Specialist  Posted: 4/14/2020 

It really depends on your free chlorine level. If the free chlorine is staying between 1-3 ppm, you won't have to "shock" it with chlorine. You could use a non-chlorine shock after someone uses the pool.

 Posted: 8/20/2018 

Hello Joan - when using Cal-Hypo shock, it should be pre-mixed before adding it to the pool. Cal-Hypo is a strong enough shock to where it can bleach out your liner if left undiluted.

 Posted: 8/4/2018 

We currently have a in-ground vinyl lined pool,we originally were shocking with a Cal Hypo type of shock from pool store and the bucket stated no pre-mixing needed, just broadcast directly to pool. Is that the best type of shock to use for a vinyl liner ? Do you think the ones that state no premixing needed are OK to use? Thank you so much.

 Posted: 7/27/2018 

Hello Jacqueline - You will definitely need to shock the pool if you intend to keep the current water in the pool. We'd recommend a cal-hypo or liquid chlorine shock. We also recommend reading our blog titled "How to Clean a Green Pool".

 Posted: 7/26/2018 

We have a 10,000 (approx) gallon in-ground pool. It came with the house which was vacant for 6 years. The pool was winterized and covered. The water is green/black. We were told that we might want to shock it before we start the cleaning process. Would you recommend this?

 Posted: 7/18/2018 

Hello Scale Last Year - Calcium hypochlorite can lead to calcium scale. If scale has been an issue, we recommend using sodium hypochlorite (liquid chlorine).

 Posted: 5/21/2018 

Last year we had a calcium scale problem in the shallow end of our pool. We had used calcium hypochlorite to shock the pool. Would that have caused the scaling and, if so, what shocking product do you recommend?

 Posted: 1/7/2018 

Anonymous (shock) - Here is the link to the Calcium Hypochloride Shock that we sell. We feel it is one of the best brands in the market.

Anonymous  Posted: 1/2/2018 

Which is the best brand granular calcium hypochlorite to use?

 Posted: 7/16/2017 

Would you use a non chlorine shock on a commercial pool.We use a non chlorine shock with 3 inch Tablets Di chlor.Its hard to get a chlorine reading.It takes severial minute for the results ,Why.Its 40.000 vinyl DE filters.

InyoPools Product Specialist  Posted: 6/9/2017 

Denese - Yes, you can you any of the shock options in a salt pool including liquid chlorine.

 Posted: 6/8/2017 

Can I use liquid pool shock in salt water system at spring start up

InyoPools Product Specialist  Posted: 7/25/2016 

dawn - See our guide on "Above Ground Pool Maintenance - step 8". Steps to emphasize - this may take several days to eliminate all the algae:
Get your water flowing and leave the pump running continuously until water is clear.
Get any large debris out of the pool with a net.
Add shock to get the chlorine level up to 10 ppm.
Check the chlorine level twice a day. Add more shock if it goes below 5 ppm.
Clear the filter twice a day to remove embedded algae.
Brush the entire pool once a day.
Continue to monitor the Chlorine level until the pool is clear. Then maintain Chlorine at 3-5 ppm
Check chemical balance especially pH and CYA levels.


 Posted: 7/23/2016 

I have a round metal frame pool 12 by 36.I filled it up 3 days ago it's already green.I bought some pool essentials shock and a 3-way test kit.I don't know anything about this stuff I haven't even turned pump on since I got it .HELP PLEASE!!

Anonymous  Posted: 5/10/2016 

Thank you for explaining the different types of shock. Very helpful.

InyoPools Product Specialist  Posted: 7/24/2014 

merbear - The most important consideration to avoid heater corrosion is to keep the high concentration of chlorine from getting into your heater. If you have a chlorinator or salt chlorine generator, make sure they are placed into your piping after the heater as the last unit in the return piping. And place a check valve between the chlorinator / SCG to prevent high chlorine water from backing up into the heater when the pump is shut off. The type of shock you use does not affect heater corrosion as far as I know. Lastly make sure you maintain water balance to reduce corrosion over time.

 Posted: 7/23/2014 

We gave an above ground pool with a gas heater. We have been told conflicting info on which aspect of chemistry us most important to avoid heater corrosion. With respect to shocks and calcium levels can anyone advise what type of shock is best? Help!

 Posted: 6/5/2014 

Thanks for the helpful info.I now know I have not been shocking my pool because Ive always used non-chlorine shock. On the up side I never had any problems.