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 raises free chlorine levels to destroy algae, chloramines, bacteria, and contaminants—essential maintenance for keeping water clean and safe. Perform shocks every couple weeks during swimming season, plus five critical circumstances (opening, parties, weather, sunny days, closing), following proper safety protocols to restore proper chemical balance and crystal-clear water.

Six essential facts about when and how to shock your pool:

  • Three general shock triggers: Algae begins growing in water, free chlorine level reaches zero, chloramines (combined chlorine) exceed 0.5 parts per million—shock when water tests outside recommended 1-3 ppm free chlorine range
  • Five special circumstance shocks: Opening day (algae growth over winter), pool parties (bacteria from heavy swimmer load), inclement weather (rain/wind contaminants and pH disruption), consecutive hot sunny days (heat intensifies bacteria growth), closing day (head start for next season)
  • Chlorine type distinctions critical: Free chlorine sanitizes and disinfects water (target 1-3 ppm), combined chlorine is chlorine bonded to contaminants creating strong odor and eye irritation, total chlorine equals free plus combined amounts
  • Important smell misconception: Strong chlorine smell indicates improperly treated water (combined chlorine problem), clean pools are virtually odor-free, don’t assume heavy chlorine smell means clean pool—opposite is true
  • Step-by-step shock process: Uncover/skim/vacuum/brush pool surfaces, wear protective goggles/gloves/work clothes, balance pH levels first, prepare shock in 5-gallon bucket with pool water and stir, run pump while pouring around pool edges, allow 6+ hours circulation
  • Post-shock waiting period essential: Test water after 6+ hour pump circulation, confirm free chlorine levels return to safe 1-3 ppm range before swimming, never enter pool immediately after shocking regardless of appearance, patience ensures swimmer safety

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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