How Long Should You Run Your Filter After Shocking Your Pool?

First of all, “Shock” is not a product, but a method.  You may be thinking, “Wait!  I have a bag that literally says ‘Shock’ on it.”  And you probably do.  The reason is, if one were going to “Shock” their pool, that is a product they could use to achieve that method. They can typically also be used as a maintenance product with a smaller dose. Are you…shocked?

What is “Shocking” the Swimming Pool?

The process of “shocking” a pool is simply adding either chlorine, or non-chlorine, products to raise what is known as the “free chlorine” level. Keep in mind the goal is to raise it to it’s killing point for chloramines, bacteria, algae and other contaminants .  When you test a pool’s chlorine, you can check for Total Chlorine (The total amount of chlorine in a pool, including chloramines), Free Chlorine (The chlorine that is free and available to keep your pool safe) and Combined Chlorine (the difference between Total Chlorine and Free Chlorine aka Chloramines).

Chlorine Shock

Since we now know “shock” is a method, let’s talk about the different kinds of shock.  One can “shock” their pool with a chlorinated product such as  liquid chlorine or granular chlorine (Trichlor, Dichlor and Calcium Hypochlorite).  Each one has a different strength and is intended for different vessels.  For example, Calcium Hypochlorite is only for in-ground, plaster pools.Consult the product’s label and/or a pool professional if you are not sure which product should be used in your pool or spa.  

Non-Chlorine Shock

Potassium Peroxy Mono Persulphate (KHSO5) is also known as Non-Chlorine “Shock”.  This has zero chlorine in it and simply oxidizes the contaminants out of the water, releasing any Combined Chlorine and turning it into Free Chlorine.  You can typically go back into the water after 15 minutes or so.  Use this product if your Total Chlorine level is fine and you just want to oxidize.  Use it if you have any combined chlorine.  And I tell my spa owners, especially Bromine spa owners, to add some after every use.  Why add extra sanitizer if you don’t need to?

Reasons to “Shock”

  •  If you have chloramines. They can be irritating to the swimmers and are the ineffective form of chlorine.
  • If you just filled up your pool with new water, or your chlorine is at zero.  We need to add enough chlorine to kill off the contaminants and organic load and still leave you with a Free Chlorine Level (FAC) of 2-5 ppm (parts per million).
  • Algae.  Getting rid of algae requires adding large amounts of chlorine, paired with an algaecide.  See our blog on “Green Pools” for step by step instructions.
  • Dead animals.  While a chlorine level of 1 ppm should be adequate in killing off any bacteria, most swimming pool owners wish to be certain after finding a dead animal in their pool or spa.  If it was a racoon you DEFINITELY want to shock because they carry a disease called Baylisascaris, which can be deadly.
  • Poop.  Whether human or animal, you’ll want to shock your pool and stay out of it for a while.  This gives the chlorine time to kill off germs and get lowered to an acceptable range.
  • At a party.  Ever been at a pool party and the water becomes cloudy?  That is because the chlorine has been doing its job and combining with contaminants like ammonia and nitrates.  Using a non-chlorine shock will free up that chlorine.  Just don’t forget to call everyone out for a 15 minute potty/snack break.  Never add chemicals when people are in the pool
  • After using your spa.  As mentioned above, using a little bit of non-chlorine shock after every use will keep your sanitizer free and available to do its job.  One can get very sick in a hot tub.  The smaller size of the vessel and the warmer temps are breeding grounds for lots of water borne diseases.

When Do I Use One or The Other?

This is a great question, and one I get a lot from my clients.  Since both products oxidize, it all depends on the goal of “shocking”.  If you need to break down contaminants and add to your chlorine level, use a chlorine product.  If your sanitizer level is fine and you just need to oxidize, then go for the non-chlorine product.

How Long Until I Can Get In? How Long Should I Run My Filter?

With non-chlorine shock, 15 minutes is sufficient with the pump running.  With using a chlorine shock, it depends on how, and what, you were “shocking” for.  A maintenance dose per say, one would only need to wait approximately 4 hours with the pump running.  A shock to raise chlorine or to kill algae? 24 hours with the pump running is about right.  After an AFR (accidental fecal release) it could be up to 72 hours of waiting and pump run time. The simplest answer is when the chlorine has come down to a safe range for swimming, which is 5ppm or lower.  Make sure you test the water to ensure that chlorine levels are not too high before going for a dip.  You should be running your pump at the same time you are waiting.  For example during an algae treatment, it is 24 hours (Or until  the chlorine is below a 5 ppm).  See you poolside!