how to do a pool shock

When and How to Do a Pool Shock

how to do a pool shock

What Does it Mean to Do a Pool Shock?

When you do a pool shock, you are raising the level of the free chlorine by adding chlorine or non-chlorine chemicals to the water. The chlorine level needs to be raised to the point where algae, chloramines, and other bacteria and contaminants are destroyed.

Just because a pool smells strongly of chlorine doesn’t mean it is clean. In reality, when a pool is clean, it is virtually odor-free. If the chlorine smell is strong, that is a sign the water is improperly treated.

Pool shocking is a planned chlorine boost that destroys algae, chloramines, and contaminants. Do it every couple of weeks in swim season (and after key events), then circulate, retest, and only swim once free chlorine is back in the safe range.

  • When to shock: Shock about every couple of weeks during swimming season, and any time testing shows you’re outside the recommended 1–3 ppm free-chlorine range. It’s also recommended for opening day, after pool parties, after inclement weather, after consecutive hot sunny days, and at closing.
  • Know the numbers: Target free chlorine at 1–3 ppm; shock when free chlorine hits zero or when combined chlorine (chloramines) rises above 0.5 ppm. A strong “chlorine smell” is often a sign of combined chlorine—not a clean pool.
  • Prep and protect: Uncover, skim, vacuum sediment, and brush walls, floor, and coves first. Wear protective goggles, gloves, and work clothes, and balance pH before adding shock.
  • Mix and add correctly: Dissolve shock in a 5‑gallon bucket of pool water and stir, then run the pump while you pour the mixture around the pool’s edges to distribute it.
  • Wait before swimming: Keep the pump circulating for 6+ hours, then test again and don’t swim until free chlorine returns to the 1–3 ppm range—never jump in immediately after shocking, even if the water looks clear.

When Should I Do a Pool Shock to my Backyard Pool?

a pool technician testing chlorine levels in the pool to determine whether he needs to do a pool shock

There are three general rules of thumb here:

  • Do a pool shock when algae begin to grow.

  • Do a pool shock when the free chlorine level of your pool is zero.

  • Do a pool shock when the chloramines or combined chlorine level rises in excess of 0.5 parts per million (ppm).

Typically speaking, you should do a pool shock every couple of weeks during the swimming season. Also, you should do a pool shock when the water tests outside of the recommended free chlorine levels of 1-3 ppm. Chlorine levels are raised by shocking the pool.

Experts also recommend a pool shock under these circumstances:

  • 1) On opening day. Before anyone jumps into your pool at the start of the swimming season, be sure to clean and shock your pool. Algae will most likely have grown over the winter months.

  • 2) When you have a party. Are friends and family expected for a big pool party? Just remember that everyone who enters your pool brings bacteria with them. During heavy use, the free chlorine levels tend to drop significantly. To restore it to normal levels, be sure to complete a pool shock.

  • 3) During inclement weather. Heavy rains and high winds can do a number on your pool water. Your best defense against these acts of nature is to clean your pool and add shock, which removes any contaminants and restores proper pH levels. Be sure to reduce the water level back to normal before adding a pool shock, however.
  • 4) On sunny days. No one is complaining about a perfect summer day, but hot and sunny days – especially when repeated on end – can alter the chemistry of the water, causing dangerous bacteria and contaminants to grow as the heat intensifies. Do a pool shock to disrupt the combined chlorine and restore it to free chlorine.

  • 5) On closing day. Those warm and sunny days eventually come to an end for the season. When you are ready to close down your backyard pool for the winter months ahead, be sure to clean it and shock it. This will give you a head-start when the pool season rolls around again next year.

Types of Chlorine

When you are testing the chlorine level of your pool, it is important to know the differences in how chlorine is classified: free, combined, and total.

You can learn more about the different types of chlorine sanitizers here and how they work.

What is free chorine?

This is the chlorine required to sanitize and disinfect the pool water.

What is combine chlorine?

This is the chlorine required to sanitize and disinfect the pool water.

What is total chlorine?

This is the total amount of chlorine, which includes the free and combined chlorine.

How to Shock Your Backyard Pool

Shocking your pool is not as difficult as it may seem.  First, you have to uncover your pool, skim it, vacuum and sediment and brush the walls, floor, and coves. Before you add any shock, protect yourself by wearing protective goggles, gloves, and work clothes.

  • First, ensure the pH levels in your backyard pool are balanced.

  • Next, prepare the shock in advance. Use a five-gallon bucket of pool water and stir.

  • Then, make sure the pool pump is running.  Pour the contents of the bucket into the water around the edges of the pool.

  • Finally, allow the pool pump to run for roughly six hours (or a bit more!) and then test the water. The free chlorine levels should be at 1-3 ppm before you get into the pool.

Once the water tests appropriately, then you can jump in and enjoy the water.

If you have any questions or concerns about shocking your backyard pool, consult your local dealer at Leisure Pools. To find your local fiberglass pool dealer, call 855-857-7527 or go to our website at at leisurepoolsusa.com. A clean and healthy pool is a happy pool and will allow you to enjoy a “life of leisure” every day.

Michael Kennedy, Chief Sales Officer at Explore Industries,

Meet our expert.

Written by Michael Kennedy.

Chief Sales Officer at Explore Industries

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