How To Choose The Right Type Of Swimming Pool Shock

WRITTEN BY:  Alex V.

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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.

Step by Step

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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, unstabilzed 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 pin holes 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.

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.

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.

Comments

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(1 to 19 of 19)

Matthew  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.
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Joan  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.
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Inyopools.com  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".
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Jacqueline  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?
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Inyopools  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).
 Reply

Scale last year  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?
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Inyopools  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.
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Anonymous  Posted: 1/2/2018 

Which is the best brand granular calcium hypochlorite to use?
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Hidden Valley  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.
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InyoPools Product Specialist Dennis R.  Posted: 6/9/2017 

Denese - Yes, you can you any of the shock options in a salt pool including liquid chlorine.
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Denese  Posted: 6/8/2017 

Can I use liquid pool shock in salt water system at spring start up
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InyoPools Product Specialist Dennis R.  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.


 Reply

dawn  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!!
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Anonymous  Posted: 5/10/2016 

Thank you for explaining the different types of shock. Very helpful.
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InyoPools Product Specialist Dennis R.  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.
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merbear  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!
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Belle  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.
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chris  Posted: 11/6/2013 

thank you for commenting on cyanuric acid with respect to the non-chloride shock. This helps people tackle the chloroamine problem with confidence.
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GeorgeYBeatriz  Posted: 12/19/2012 

Thank you this was a lot of help
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