What Does Pool Shock Do

What Does Pool Shock Do?

You must do specific tasks to keep your pool clean, and one of those tasks is pool shocking. Shocking your pool helps keep it safe and clean for the best possible swimming experience. So, what is pool shock, and what does pool shock do?

Shocking your pool is simply the process of raising the “free chlorine” level of your pool to prevent contaminants. This article will cover what pool shock does, types of pool chlorine, and how to shock your pool.

What is Pool Shock?

Pool shock is adding chlorine to the water to boost the “free chlorine.” Raising your pool’s free chlorine level is a simple way to keep your pool free of bacteria and algae.

What Does Pool Shock Do?

The goal of pool shock is to raise the pool chlorine level to a point where bacteria, algae, and other contaminants are destroyed. However, note that a pool isn’t necessarily clean because it has a strong chlorine smell. The first indicator of clean water is a pool with almost no odor.

A strong chlorine smell indicates that the water hasn’t been correctly treated. The odor source is chloramines, commonly known as mixed chlorine. Chloramines are created when nitrogen in urine, oils, and sweat mixes with chlorine.

Types of Chlorine

what does pool shock do

Knowing the differences between the various types of chlorine is essential as you learn how to shock a pool. Let’s have a look:

Free Chlorine (FC)

FC is the amount of chlorine that is actively used to disinfect water. For the chemical to function correctly, free chlorine levels must be between 1 and 3 parts per million (ppm).

Combined Chlorine (CC)

Combine chlorine is the chlorine that’s been used. Although the CC remains in the water, it has little sanitizing power. Keep the CC level in your pool at or below 0.2 ppm.

Total Chlorine (TC)

This is the sum of the CC and FC in your pool. Pool testing kits can help you accurately measure the TC and FC of your water. However, you can get your CC value by subtracting the FC from your TC.

Breakpoint Chlorination

This happens when there is enough FC to break the bonds between the chloramine molecules. The free chlorine in your pool water may accumulate once you reach breakpoint chlorination. Note that free chlorine does all the work when disinfecting a pool.

When shocking your pool, always try to reach the breakpoint. Shocking your pool without reaching the breakpoint will cause chloramine to build up. If you let chloramine build up in your pool, it may eventually become smelly, requiring a partial or complete water replacement to address the problem.

How to Shock a Pool

By shocking a pool, free chlorine levels are boosted ten-fold compared to combined chlorine levels. Note that you’ve achieved the breakpoint chlorination when you reach this mark. Here are tips on how to shock a pool:

  • Get your timing right. Shocking your pool when the sun is up may cause any unstabilized chlorine to burn off. Therefore, ensure you shock your pool at night, so the chemicals can work properly.
  • Checking your pool’s PH level should be your first big step. Get a pool test kit and measure your water’s FC and TC levels. Next, find your pool’s CC level by subtracting the FC from the TC. Knowing your pool’s FC, TC, and CC levels will help you determine how much chlorine to add to the pool.
  • Do the math to determine how much shock you’ll need to mix. You can get this information by looking at your shock chemical package for the indicated amount.
  • Next, confirm if your granular pool shock requires mixing with water before use. If not, you can add it directly to your swimming pool. If your granular pool shock requires mixing, ensure you do it beforehand to save time and prevent calculation errors.
  • Check if your pool pump is working, and then pour the shock mixture around the pool’s edges. Leave the pump running for at least six hours.
  • Test the chlorine levels of your water to ensure that it is within the appropriate range. Wait for the pool’s FC levels to drop to 1 to 3 ppm before taking a swim.

Tips: Ensure you wear your safety glasses and gloves while working with pool chemicals.

How Often Should You Shock a Pool?

The smell or eye irritation should not be the only indication that you need to shock your pool. In general, you should shock your pool when:

It is recommended that you shock your pool at least once a week. However, you may need to perform a pool shock afterward:

  • A severe rainstorm
  • Someone peed in the pool
  • Significant water level change
  • A pool party or other heavy pool use


Shocking your pool regularly helps keep its water clear and fresh. Also, this practice helps to keep algae, bacteria, and other contaminants away from your pool. Ensure you measure your pool’s chlorine levels and reach breakpoint chlorine when shocking your pool.