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It sounds, well, shocking, but shocking a pool is not really as outrageous as the name implies. In fact, every pool owner should know how to shock a pool, because it’s an important part of pool maintenance. Here, we’ll explain pool shocking, and how to do it correctly.

Shocking your pool is just a matter of rebalancing the chlorine levels, so that your pool water stays sanitary and safe for swimming. It’s done using a super dose of pool chlorine that kills bacteria and oxidize chloramines in the pool by depleting combined chlorine and increasing free chlorine. There’s actually chlorinated shock, used when chlorine levels are low, and non-chlorinated, for when the chlorine is already high. It’s best to shock a pool at night, when the sun isn’t shining, so that UV rays won’t reduce the effectiveness of the chlorine.

Why is it necessary to shock a pool? Chlorine destroys the contaminants in your pool, but over time it weakens. Levels of combined chlorine, known as chloramines, begin to rise, and these can be irritating to the skin, eyes, and lungs. Additionally, pollutants in the pool may increases because of rainfall, debris from the yard, and organic matter from people swimming in the pool. Algae can also bloom in the pool, and while algaecide can control them, shocking the water will clear it of algae. If the water is cloudy because of unbalanced pool chemicals, a shock can restore clarity.

So, what’s the right way to shock a pool?

  • First, test the water. Use a pool water testing kit and balance the levels, making sure the pH is between 7.2 and 7.6 and the total alkalinity is between 80 and 120 ppm. Add more chemicals as necessary to raise or lower the pH until the level is neutral.
  • Use caution when using chemicals. Gloves, eyewear, and old clothes are a must, because chlorine fumes can be irritating, and chlorine can bleach fabric. Mishandled, chlorine can be hazardous not only to you, but also to your pool deck.
  • Calculate the right amount of shock for your pool. Typically, you’ll need a pound of shock for every 10,000 gallons of water, and shock is sold in one pound bags. You can calculate your pool’s capacity by multiplying the length times the width times the depth times 7.5, and it will probably be 10,000 or 20,000 gallons, making it easy to determine how many bags to buy. You’ll want to follow the directions carefully, as not all shock is the same, and you’ll also want to make sure you’re adding 10 times the amount of the chloramine level. To determine the chloramine level, test the water and subtract free chlorine from total chlorine.
  • If you’re using granular shock, mix it in a bucket. A five gallon bucket is perfect for this project. Just fill it about three-quarters full and add a bag of shock. Always put the shock in second, not first. Stir with a wooden stick until the shock is dissolved. Then you can add it into the pool, pouring it slowly around the perimeter of the pool. Liquid shock can be added into the water directly, poured around the perimeter of the deep end. If you’re using granular shock, check to make sure there are no undissolved granules on the walls of the pool, then make sure your pump and filter run all night, to fully distribute the shock.
  • You may need to shock it more than once. If the pool is very large, or overrun with algae, shocking it more than once may be necessary. It’s important to know how long to wait after a pool shock to shock it again. Because a shock needs to be done after the sun has gone down, you’ll need to wait at least 24 hours before doing it again.
  • There’s also the question of how often to shock pool water. There is no hard and fast rule for this, because it depends on a variety of factors, like how much rain you’ve gotten and how many people have been using your pool. If your water is cloudy or has algae growth, you’ll know it needs to be shocked, but because most pollutants are invisible, you’ll want to get on a regular schedule. Some pool owners shock their water once a week, while others do it once a month. Checking your chemical balance frequently will help you gauge how often you need to shock yours.

Do you want to know how long to wait after shocking pool water before swimming? This is another question that has no solid answer. Typically, you’ll want to wait at least eight hours, but it really depends on your chlorine levels.  It’s certainly not safe to swim with ten times the chlorine, so you’ll want to test and make sure it’s back to normal before you take a dip.

When you need someone to help maintain or repair your pool, Millennium Pools and Spas can help. With over 30 combined years of experience in the pool industry, we provide a comprehensive range of pool services for both residential and commercial customers in Virginia, Washington DC, and Maryland. When you hire Millennium Pool Service, you get a well-qualified, industry-trained staff of pool contractors and technicians, services that are tailored to your needs, and a commitment to 100% customer satisfaction. Contact us for more information.

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