How to Shock a Swimming Pool or Hot Tub

Shocking your pool should be part of your regular maintenance. It will help you avoid algae and bacteria build-up, and save you from cloudy water.

The goal in shocking your swimming pool or hot tub is to ultra-chlorinate the water, kill off the chloramines, and rid bacteria from floating around. The most important times to do so are in the beginning of the swimming season and after high amounts of activity, like a pool party. This article describes how to shock your swimming pool, and provides considerations on which shock to choose.

To keep your swimming pool healthy and pleasant, shocking your pool should be apart of your weekly or bi-weekly maintenance. Keeping up on this regular maintenance will avoid algae and bacteria build-up, ultimately saving you from cloudy water. There are many liquid pool shock kits that claim to get the job done. Some may advertise to clear your pool in one sitting, but before you decide to invest in a liquid pool shock kit, there are chemistry basics in the mix you need to know. 

Why do I Need to Shock my Pool?

As mentioned before, shocking your pool should be apart of your weekly maintenance. Even if the water looks crystal clear, it is not an accurate indication of chemical balance within the swimming pool/hot tub. Whether the bacteria is man-made or the chlorine is diluted from natural causes, your pool will need help in staying clean and clear. High activity in your pool releases sweat, makeup, and other humanly bacteria, and needs to be combated with high amounts of chlorine. When it comes to issues that can be tied to nature, watch out for days with heavy rainfall and days with lots of sunshine. During hot summer days, the sun breaks down the chlorine in your pool by 5ppm per day. Just as the sunshine causes you to lose free chlorine, rainy days also dilute the amount of chlorine in your pool.

Before Shocking your Pool, Think About:

  • Using pH test kits to get a read on the current chemical balance of your pool (test strips don’t account for amounts of total or combined chlorine)

When your free chlorine level drops below 3ppm, it’s a good time for you to shock your pool. If you want to know more about the differences between free chlorine, total chlorine, and combined chlorine, check out our blog post here: What is Free Chlorine, Combined Chlorine, and Total Chlorine?

  • Set aside time in the evening to shock your pool (as mentioned before, the sun can break down up to 5ppm of chlorine per day. so, make sure to begin shocking your pool when the heat of the day has passed, or as the sun is setting.)

  • Consider What Type of Pool Shock Kit is Best for you: 

Calcium Hypochlorite (AKA Cal-Hypo Shock)

Cal-Hypo Shock is like a bottom shelf liquor- it’s cheap and it’s strong. This type of pool shock kit usually comes in a granular form. It needs to be mixed in a bucket with warm water before it enters your pool.

“The free chlorine generated from calcium hypochlorite helps provide clear water by killing algae and by destroying organic matter that will cloud the water if allowed to build up. Chloramines, the most common cause of unpleasant odors, are also eliminated by the action of free chlorine.”

-Association of Pool and Spa Professionals,%202014.pdf 

Because Cal-Hypo Shock dissolves quickly, it’s cleaning power is somewhat on a timeline. While this type of pool shock kit is very strong, it’s also the most sensitive to sunlight. To maximize the effects of Calcium Hypochlorite, avoid application in direct sunlight.

Sodium Dichlor (AKA Di-Chlor)

Like Calcium Hypochlorite, Di-Chlor is also a granular pool shock kit. Unlike Cal-Hypo Shock though, Sodium Dichlor is a slow dissolving mix, which maximizes and extends the cleaning power. It contains a balanced pH level and holds zero amounts of calcium, which means it increase the “hardness” of your pool water. Be conscious of the effects to the cyanuric acid levels in your pool. While the lack of calcium may help with pool hardness, using Sodium Dichlor as a pool shock can cause Cyanuric Acid levels to rise.

Lithium Hypochlorite

Lithium Hypochlorite is a type of liquid pool shock. Liquid shock kits like this one will save you time in your maintenance schedule. One must take note that Lithium Hypochlorite doesn’t contain any calcium in itself. If your pool has high calcium indications, this may be the liquid pool shock kit for you.

“Its primary pesticidal use is to control algae, bacteria and mildew in swimming pool water systems, hot tubs and spas…”


Potassium Peroxymonosulfate (non-chlorine shock)

Safer for vinyl-lined pools, Potassium Peroxymonosulfate is a salt-based oxidizer. Because there is no chlorine content in this pool shock kit, it doesn’t kill bacteria. Instead, it oxidizes the organic matter in the pool. Non-chlorine shock works by killing the dead chlorine (chloramines) and allows the remaining free chlorine to attack algae and bacteria. While non-chlorine shock kits obtain lesser cleaning power, they are a safer alternative to using chlorine.

Materials Needed to Shock your Pool:

  • Protective eyewear
  • Mixing bucket (to mix pool shock and warm water)
  • pH test kit
  • Pool Shock kit (of your choice)
  • Patience!

Try out our Pool Calculator as you clean and maintain your pool! For more information on how to care for your swimming pool, see our blogs on Pool Maintenance

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