How to Shock a Pool (and Why)

What is Pool Shock Treatment?

Shocking a swimming pool is a process that involves adding chemicals to the water. It’s done by adding shock, which is a granular or liquid pool chemical designed to eliminate bacteria, algae, and other organic contaminants in your pool water. Essentially, it's a more concentrated form of chlorine than what you use for regular pool maintenance, as what it’s doing is giving your pool water a necessary jolt of chlorine. Like the caffeine burst of espresso, for your pool!

Signs You May Need to Shock Your Swimming Pool:

• Algae is visibly growing in the water or on the walls
• Your pool water is cloudy
• The chlorine level in your pool is low (the ideal level being 1 to 3 ppm)
• Your skin itches while in the water, or after a swim
• The water has a strong chlorine smell
• It’s the beginning of pool season, and it’s always a good idea to open with a chlorine shock

Remember, there is no harm to preemptively shock at certain times to ensure high water quality and safety.

How Often Should You Shock Your Pool

When your pool is uncovered and exposed to the natural elements, we suggest shocking your pool every week or two. You may need to shock more often if it’s hot outside, or in regular use.

In addition, following heavy use like a pool party, you may want to shock to remove any contaminants that may have been introduced to the water.  Similarly, after heavy rainfall it’s also recommended, or any time the water’s visibly cloudy.

What Equipment is Needed for Pool Shocking

You’ll of course need what’s actually called shock to give your chlorine the requisite jolt.

It typically comes in pre-packaged bags already formulated, or in a large bucket that needs to be mixed. The most common types of pool shock powder are calcium hypochlorite, lithium hypochlorite, dichlor, and potassium peroxymonosulfate, though there are others.

You can buy shock at pool stores, hardware stores of all sorts, or online. 

Other than that you will need a pool test kit to measure the free chlorine and combined chlorine levels in your pool water, to determine how much shock you need to add.  

Plus a bucket to mix the pool shock with water (depending which type you bought), as well as gloves and safety glasses for protection from pool chemicals.

You’ll also want a pool brush to scrub the pool walls and floor after shocking, to loosen any algae or contaminants that may still be clinging to the surfaces. Or if you have a robotic pool cleaner like a Dolphin, it can do this scrub instead.

Steps for Pool Shocking

When you're shocking a pool, the goal is to raise the free chlorine level to approximately 10X the combined chlorine level. This is known as breakpoint chlorination.  

1. To begin, gather your supplies including the pool shock you chose, a pool test kit to measure chlorine levels, and your safety gear.
2. Test the water to see your current chlorine levels and determine the amount of shock you need to add.
3. Prepare the shock solution, or simply measure out the amount needed. Remember, you’ll generally need 1 pound of shock per 10,000 gallons of pool water.
4. Make sure the pool pump is running.
5. Pour the shock mixture into the water, around the edges of the pool. 
6. Let the pump run for about 6 hours or more, to ensure that the shock is thoroughly distributed and that contaminants are eliminated.
7. Test the pool water again to make sure it’s now at the proper chlorine level.
8. Then wait for the free chlorine level to drop to 1 to 3 ppm before going back in the water.

Although it’s not difficult, if you’re unsure about how to shock your pool, or feel uncomfortable following the steps, it’s best to consult with a pool professional first.

Tip: It’s generally considered best to shock your pool in the evening hours, so the sunlight doesn’t interfere with the chlorine treatment.

Other Tips for Keeping Your Pool Clean

To minimize the need for shocking in the first place, robotic pool cleaners can also help.

Make sure you’re also keeping all pool chemicals balanced, bugs and leaves out of the water, and the pool filter clean. For tips on that, you can also read The Ultimate Guide to Pool Maintenance.

Conclusion

While pool shock treatment is an important part of keeping your pool clean, it’s only part of the ongoing maintenance required. Keeping to a set schedule of surface cleaning, shocking, checking the chemical levels, as well as regular physical evaluations, are going to be your most powerful tools for ensuring sparkling, safe swimming water.