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How to Shock a Swimming Pool

You should shock your pool every week or two with the correct amount of shock, but what is shock?

Shock Treatment – The addition of an oxidizing compound or a mixture of oxidizing compounds to the water to destroy chloramines and other undesirable compounds. – Bioguard

When you add chlorine to your pool, the chlorine molecules attach themselves to bacteria and other unwanted material, and it forms a chloramine. Chloramines are essentially dead chlorine. They do nothing and you should get rid of them – this is where shock comes in.

Shock oxidizes the chloramines turning it into a gas. When you smell chlorine, you are smelling chlorine that is NOT in the water because it’s oxidized.

How to Shock a Swimming Pool

Now that we’ve given you the reason on WHY you should shock your pool, let’s talk about how to shock your pool.

4 Types of Pool Shock

There are 3 different types of pool shock on the market today:

It is important to understand the difference between these 4 types of shock, as they all work differently.

Calcium Hypochlorite

This is the most popular chlorine pool shock. It contains about 65% available chlorine and is cheaper than the rest. When adding to the water, you must first pre-dissolve each pound in a 5 gallon bucket of water to prevent bleaching. This type of shock is slow dissolving, so it will not completely dissolve before it hits the bottom of the your pool. Once added, you will need to wait 8 hours before swimming.

  • 65% chlorine
  • Pre-dissolve required
  • 8 hour wait time
  • Adds calcium to the water
  • Add at night
In The Swim Chlorine Pool Shock - 24 X 1 lb. bags
List Price: $83.99
Price: $66.99
You Save: $17.00 (20%)

A very effective pool shock that uses calcium hypochlorite (chlorine) to instantly kill bacteria in your swimming pool.

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Lithium Hypochlorite

This type of shock is commonly used in areas that have a high amount of calcium in the water since this shock doesn’t use calcium. It contains about 35% available chlorine and is more expensive than using calcium hypochlorite. The one positive is you don’t have to pre-dissolve this type of shock, but you still need to wait 8 hours before swimming.

  • 35% chlorine
  • No pre-dissolve
  • 8 hour wait time
  • Add at night
In The Swim Lithium Pool Shock - 24 x 1 Pound Bags
List Price:
Price: $174.99
You Save:

A very effective pool shock that uses lithium hypochlorite to instantly kill bacteria in your swimming pool.

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Di-Chlor (Grandular Chlorine)

Grandular chlorine is simply 60% chlorine that you can pour directly into the water. You will need to wait 8 hours before swimming again, but no need to pre-dissolve and it contains cyanuric acid (chlorine stabilizer) that protects the chlorine from being burned off by the sun. It’s more expensive than calcium hypochlorite, but you can use it for regular chlorine dosages and shock treatments.

  • 60% chlorine
  • No pre-dissolve
  • 8 hour wait time
  • Adds cyanuric acid to the water
  • Add at night
Nava 1-1301-24 24-Pack Chlorinating Shock Treatment for Swimming Pools, 1-Pound
List Price: $119.99
Price: $103.78
You Save: $16.21 (14%)

A very effective pool shock that uses di-chlor to instantly kill bacteria in your swimming pool.

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Potassium Peroxymonosulfate (non-chlorine shock)

Non-chlorine shock is typically used in bromine pools, but you can use it in chlorine pools as well. You do not need to pre-dissolve and it only takes 15 minutes before you can swim again. However, this type of shock can get very expensive.

  • No chlorine
  • No pre-dissolve
  • 15 minute wait time
  • Add anytime
In The Swim Chlorine-Free Pool Shock - 24 x 1 lb. bags
List Price:
Price: $69.99
You Save:

An effective pool shock that allows you to swim 15 minutes after shocking.

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How to Shock a Pool: Quick Tips

  • Always use gloves and protective eye wear.
  • Add 1 pound of shock a 5 gallon bucket of water about 3/4 full.
  • Always add shock to water not water to shock.
  • Wear clothes you don’t care about – they might get bleached.
  • Warm water dissolves shock faster than cold.
  • DO NOT add shock directly to your skimmer!
  • Use a wooden stick and slowly stir in the shock making sure it dissolves completely, or as much as possible.
  • Slowly pour the bucket of pre-dissolved shock around your pool. You may have some undissolved shock at the bottom of your bucket. In this case, just dip your bucket in some pool water give it a slow swish around and pour it back into the pool to help dissolve some of that shock.
  • DO NOT mix all the bags together in one bucket.
  • Always shock at dusk or night time. The chlorine works better when it’s not being burned off by the sun.
  • Shock should also be added every week to ensure a clean and algae-free pool.
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Happy Swimming!

How to Shock a Swimming Pool

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  • Miriam Druyan

    I have to say thank you for your whole site and the newsletter – they were helpful last summer, and I’m now ‘studying up’ for this summer! Question – we have a 3 meter Intex round pool. We keep it covered at night. The nights we shock it, though – keep it covered, or will it work better if the gas can escape more easily?

  • Matt Giovanisci

    On the nights you shock, keep the cover off.

    Glad you like the site and found it helpful :-)

  • aaron

    Hi Matt: What about using liquid chlorine to shock the pool? I am a total newbie!

  • Al Barrs

    What can I use in our Baqusil pool to remove the foam. I have checked and tightened all plumbing connection and believe it is the shock treatment of algaecide I used at pool close down last fall. I had been fighting with mustard algae for a long time with no success. The product I used did takeout the mustard algae but when I opened the pool this year it is foaming. The directions were to use a double dose the first treatment…2 small packets.

  • Matt Giovanisci

    If you lower the pH, it will help with the foam temporarily. Or just wait for the algaecide to work its way through.

  • Stephen

    Hi Matt,

    Thank you for the site. It has been very helpful. I do have one question about this article- You say that the Potassium Peroxymonosulfate (non-chlorine shock) can get very expensive but the product you listed looks to be about $70 for 24 one pound bags which is only slightly more expensive than the calcium hypochlorite. Where does the extra expense come in?

  • Matt Giovanisci

    You’re welcome! Glad to hear it :-) And you’re totally right. Thank you Amazon! Guess the industry is changing. Those prices are updated from Amazon every hour.

  • Rick Taylor

    I have a salt water generator on my pool, do I shock this type of pool, and which shock do I use?

  • Matt Giovanisci

    You can use non-chlorine or calcium hypo shock. You may not have you use it as often as a non-salt user.

  • Rick Taylor

    Ok thanks, that answered my question, thank you!

  • susandudley

    How much shock for a 16x32x52 pool with a salt system?14364 gal.

  • Matt Giovanisci

    2 pounds

  • Aracely

    Is it normal that after the 8 hours are completed the water smells like chlorine? I don’t know if thats bad or you can add something else to take the smell away.

  • Matt Giovanisci

    Yes, that’s the chlorine burning off. This is totally normal. However, when you smell chlorine, that means there’s usually none in the water. Hence water parks.

  • Matt Giovanisci

    Use liquid chlorine to get rid of algae, but not as a week shock process (oxidation).

  • Matt Giovanisci

    Also, you don’t want to be lugging gallons of liquid chlorine every week or two.

  • aaron

    Ok so what should I be using instead? Our pool is 18×36 with a brominator

  • Matt Giovanisci

    Well with a brominator you wouldn’t use chlorine. I would use a non-chlorine powder shock.

  • aaron

    Wow, now I am really confused. The guy who opened our pool said chlorine is fine for a bromine pool. Too much info out there! I will investigate this powder you referred to. Thanks for your response.

  • Matt Giovanisci

    Bromine is a less powerful oxidizer than chlorine. That means you gotta stay on top of things. You can either use monopersulfate (non-chlorine shock) or chlorine shock. I recommend using non-chlorine shock though.

  • aaron

    So the non-chlorine stuff comes in pouches by the looks of it. I just pre-mix a pouch in a bucket the pour the water into the pool?

  • Matt Giovanisci

    With non-chlorine shock, you can just add it right to the water without pre-mixing.

  • aaron

    Ok thanks, Matt. I’m in Canada so you probably recommend different brands than what we have here. Any suggestions for what I should buy if available?

  • Matt Giovanisci

    See if you can find Bioguard. I always liked it, but it’s a bit more expensive than most other brands. Really, as long as it says

    Potassium Peroxymonosulfate (non-chlorine shock)
    …you’ll be good!

  • aaron

    Ok, cheers! I appreciate you getting back to me!

  • Matt Giovanisci

    You’re welcome :-)

  • Aracely

    Thank you

  • Bill Varela

    Hi Matt – I shocked my 20,000 gallon pool last night because it was green using 6 lbs of shock and have been running the filter ever since. This morning it was a little lighter but not much. I scrubbed the walls again to let the shock continue to work but not sure if there is anything else I should be doing. Please help!

  • Matt Giovanisci

    Shock it the following again with the same amount. It should be cloudy blue after that.

  • Jen

    I have a 14×42 above ground pool, new at all this pool stuff trying to learn but I’m confused about shocking. I have a bottle of shock don’t know if I prefer mix it or what it’s the granules or how much I use. Thanks.

  • Matt Giovanisci

    If you’re unsure, just pre-dissolve it just in case.

  • Kathy Stubbs

    Just purchased a Intel inflatable pool, 10×10 and holds 1000 gallons of water how much chlorine should I use?

  • Matt Giovanisci

    1/4 pound of shock.

  • Isabella Becker DeMarco

    if we add shock at night do we need to run the pool all night?

  • Matt Giovanisci

    Yes

  • Jesse Kapp

    I had my water tested and it checked out fine. Phosphates a bit high and chlorine a bit high (5 ppm). The water looks just slightly cloudy and I’m thinking it is from the fall leaves getting into the pool. Should I use shock to try to kill/clear the cloudy water even though the chlorine is already high or should I just use clarifier and filter it?

  • Gail Harding Ratchel

    Does the same rule of applying oxidizing shock at dusk or at night apply or can it be added during the day?

  • Matt Giovanisci

    It can be applied during the day. Only chlorine shock should be done at night because the sun eats the chlorine.

  • Matt Giovanisci

    If your chlorine is good, just use a clarifer.

  • Gail Harding Ratchel

    That’s what I thought, but wanted to be sure! Thanks Matt!

  • Matt Giovanisci

    You’re welcome :-)

  • Pool Aide Mosman

    You need to be careful regularly shocking with stabilized products like Di-chlor. The stabilizer will build up in the pool over time and end up locking up the chlorine so it is no longer effective.

  • Matt Giovanisci

    True, but with rain and splashout, this should even out. However, it’s a good idea to keep an eye on your CYA levels.

  • Guy Mutton

    Hi Matt, my biggest issue is my pool often goes green in the summer, and i have no ‘vacuum to waste’ option on my filter.. i got it perfectly clear over Christmas (our summer) but it just went green again after some heavy rainfall the past few months so am going to have to do something again to sort it.. apparently the phosphates are VERY high (higher than the pool shop finds in hotel pools etc).. I have just brushed it again and will try your shock treatment, and probably a clarifier (as i have found to work previously) but i am unsure how to best get the algae out of the pool without the ‘waste option’ ? It has a cartridge filter, and in the past, have just taken the top of the cylinder and let the water spill onto the ground, but it ends up going everywhere, including on the neighbour’s yard area.. what are your thoughts? Thanks

  • Lauren Renz

    I just purchased a 18’X48″ round above ground pool with a salt water system. We began to have a yellowing in the water and my filter was filthy when I went to clean it (thinking that was the cause). I just shocked it this afternoon with a 3/4 lb non-chlorine shock. How long should it take for my water to become clear again? (note I am cleaning the filter every three hours and I have no sand filter added to the system.)

  • Matt Giovanisci

    Rain can cause algae, but only if you’re sanitizer is low. Keep an eye on your sanitizer levels. Invest in a chlorinator, salt system, or something to help regulate if you can. Shocking will only kill algae, but it won’t prevent it. Keeping a balanced pool and proper sanitation will keep algae at bay.

  • Mary Lynn Callen

    I’ve been reading so much about water chemistry lately, I’m confusing myself. When I shock my salt water pool, should I turn off the chlorinator for 8 hrs, or just leave it running? I have it set to 25% right now.

  • Matt Giovanisci

    You can leave it running. But you don’t need it.

  • Jack Shaffer

    Hi Matt:

    Great website. I have an endless pool inside and for 3 years trouble free. I had a gas ht exchanger put in to save on electric heating bills and some residual oil from the ht exchanger got in the pool. I had to drain it half way and refill. But now I have cloudy water with a yellow like dust on the floors and walls. The Cl is 3, the Ph 7.5 but the TA is 250. The water also smells strong or chemicals , not necessarily chlorine smell.

    Any ideas on what to do would be helpful. So for I am being told to bring down TA first, then shock the pool, then adjust the PH.

  • Matt Giovanisci

    You could bring down the TA, but the pH is good. I would just wait it out.