Pool Shock Dosage Advice: How Much Chlorine Shock Should You Add?

Regularly using shock treatments is an essential part of good pool maintenance. Shock is instrumental in keeping your water clean, safe and free of algae, so it’s important you use the right dosages and keep all your other chemicals in check. 

What is Shock For Pools? 

Shocking your pool refers to the process of adding a high concentration of chlorine (or a non-chlorine sanitiser) to your pool water to rapidly increase the levels of free chlorine. 

The high level of chlorine kills bacteria, chloramines, algae and other contaminants. These quantities can reach as high as ten times the normal, everyday maintenance dose.

Swimming pool shock can come in several forms, including granular and liquid. These different types include sodium hypochlorite and calcium hypochlorite, along with chlorine-free oxidising shocks. 

How Often Should You Shock Your Swimming Pool?

The frequency at which you shock your pool will depend on a couple of things. Generally, it’s recommended you add shock to your pool: 

  • When first filling up your pool.
  • After spotting any signs of algae or slime.
  • After any period of heavy use.
  • After any loss of water clarity or quality.
  • After a heavy rainfall.
  • At the end and beginning of each season.
  • As part of a weekly or bi-weekly maintenance routine. 

If it gets a lot of use, it’s recommended to shock your pool every week. If you don’t use your pool every day, shocking your pool around every two weeks should be sufficient. 

Maintaining your pool chemistry and regularly balancing your other chemicals may reduce the frequency that you need to shock dose your water. 

A group playing catch in a pool

Signs You Should Shock Your Pool 

Here are a couple of symptoms that indicate your pool requires immediate shocking. 

Your Pool Has Gone Green

Green water is caused by algae growth, and pool shock is a key ingredient for clearing up this issue. The severity of your algae problem can be determined by the shade of green. 

The lighter the green, the more recent the algae growth. If the shade of green is darker, you may have a bigger, more troublesome problem on your hands. 

Shock will help eradicate the growing bloom and stop new algae growth in its tracks. You will need to be especially careful about your maintenance routine post-algae removal to ensure it doesn’t come back. 

How to prevent algae growth in your pool

Low Chlorine Levels 

Outdoor pools require a chlorine reading of 1-3 ppm. If your chlorine dips below the necessary levels for too long, your pool won’t be receiving sufficient sanitisation. 

To rapidly get things back up to where they should be, you can use a shock treatment and follow it up by regular doses of chlorine with a lower concentration to maintain a steady level. Using chlorine tablets in a floating chemical dispenser is a good way to ensure your water gets a consistent dose of chlorine in between more intense shock doses. 

Ineffective Chlorine 

Another reason you might want to reset your water’s chlorine content with a shock dose is when it doesn’t seem to be working effectively. 

Chlorine can be deemed ineffective due to either over-stabilisation, also known as chlorine lock, or a pH level that is too high. When a pH level reads 7.2, chlorine is 66% effective, but with a pH level of 7.8, the chlorine will only be 22% effective.

If you’ve got high levels of combined chlorine, it also means there’s less effective chlorine in your pool. When you get to this point, you will also have chloramines in the water, which will need to be eliminated by a shock dose. 

What's the difference between total chlorine and free chlorine

Your Pool Water is Cloudy

Cloudy pool water is a sign of poor filtration and low sanitiser levels. The cloudiness is likely due to contaminants present in your water that are not being removed via the filter or broken down by your chemicals. 

Here, you will need to use shock to tackle lingering bacteria and organic pollutants. Shock dose your swimming pool at night. This will prevent the sun’s UV rays from breaking down the sanitising hypochlorite ions, ensuring your pool receives a heavy shock dose necessary to kill off any bacteria contaminants such as E. coli and Legionella.

How Much Chlorine Do You Need to Shock a Pool? 

Once you know why and when to shock your pool, it becomes a question of how much product to add. 

As a very general rule, pool experts advise that for every 10,000 gallons or water, you’ll need to add one pound of shock. However, if your water is very dirty or you’re experiencing extreme algae problems, you may need to double or quadruple this amount to get your pool clean again. 

The exact amount of shock you require will also depend on the product you’re using; different brands and shock types will call for different dosages. It’s always best to carefully refer to the dosage instructions on your pool shock’s packaging

Below is a rogue example of how much chlorine shock you should expect to add if you want to raise your chlorine levels by 6 ppm and 10 ppm. But again, refer to your shock’s detailed instructions first and foremost. 


Pool Size Litres of 10% available chlorine Sodium Hypochlorite needed to give: Grams of 60% available chlorine Granules to give:
Gallons 6 ppm 10 ppm 6 ppm 10 ppm
5000 1 2 300 450
10000 3 5 600 900
15000 4 7 900 1350
20000 6 9 1200 1800


How Much Should You Raise Your Chlorine Levels By? 

Use the below guide to gauge how much you’ll need to raise your pool’s free chlorine levels by. The different grades show the severity of the issues and will correlate to how much shock you should add. 

Grade Pool Description Shock Treatment Chlorine
1 Pool apears clean & clear. 6 ppm No algae growth.
The floor at the deepest part is clearly visible.
6 ppm
2 Pool not quite clear. 10 ppm Traces of algae on skimmers.
The deep end of the pool is just visible.
10 ppm
3 Pool with noticeable haze. 20 ppm Shallow end floor clearly visible.
Deep end not visible.
20 ppm
4 Pool slightly cloudy. 30 ppm Shallow end floor not quite visible. 30 ppm
5 Pool pale green. 40 ppm Top 3 steps visible but no floors. 40 ppm
6 Pool distinctly green. 60 ppm Top steps only visible. 60 ppm


How to Shock Dose a Pool

To find out more about how to shock a pool once you’re confident with the dosages, head over to our guide on using shock treatments. 

How to use swimming pool shock treatments

The main thing you need to be careful about, aside from remaining mindful of safety, is testing your water. This gives you an accurate picture of your pool’s chemistry before you start adding new chemicals. 

Also make sure you keep your pump running continuously after adding a shock dose. This will ensure the chemicals are properly circulated and prevent concentrated quantities of chlorine from bleaching the liner. 

If you’re using chlorine granules, be aware that these should be dissolved in warm water first, and then added to your pool rather than being applied directly. 

We stock a great range of swimming pool chemicals and shocks to keep your pool in prime condition. Browse now to ensure your pool stays happy and healthy!