Shocking your pool at regular intervals is important but it will not be very effective if you do not run your pool pump long enough to allow it to do its work. So how long should that be?
You should run your pool pump for a minimum of 6 hours after shocking, although running it for a full 24 hours after shocking is often recommended. This is to ensure that not only is the shock thoroughly mixed around the pool but also that the filter will remove any dead germs or algae killed by the shock.
If you shocked your pool but didn’t run the pool pump then the concentrated chlorine would not be mixed thoroughly with the pool water so you would have areas of very high concentration. Not only would this mean the shocking would not be so effective but potentially the very concentrated chlorine might damage the pool.
Also, without the pump running, and therefore the filter system not working, any dead algae etc will not be filtered out.
Why should you shock your pool?
In order to maintain good water chemistry it is important to raise the free chlorine level so that the contaminants in the pool such as chloramines (chlorine molecules combined with sweat, germs and other substances), algae and bacteria are removed.
This is exactly what shocking the pool does as you are adding concentrated free chlorine to bring the levels up high enough so that it can do its magic.
I generally find it more economical to buy shock in bulk in the form of a 25lb bucket of chlorinating granules. If you refer you can buy it in 1lb bags or a liquid pool shock. All of these are available on Amazon or from your local pool store.
How to shock your pool
This is the method I use to shock my pool:
- Firstly enure the pool is clean and free from leaves and other detritus by vacuuming if necessary.
- Mix the shock in a bucket of water and stir until it is all dissolved. It may help to dissolve it all and quicker if you use hot water.
- Make sure your pump is running
- Walk around the pool pouring the shock from the bucket around the edges of the pool as you go
- Leave the pool pump running with it on the filter setting for between 6 and 24 hours. I often split the difference and run it overnight, so around 12-15 hours.
- You shouldn’t swim in the pool until the free chlorine level (sodium hypochlorite) drops below 3-5 ppm.
When should you shock your pool?
There are a number of times when you should consider shocking your pool:
- Whenever you start up at the beginning of the swimming season and before you close it at the end it is good practice to shock your pool.
- If you have very heavy rain, this can wash contaminants into the pool. So it can be a good idea to shock the pool prior to it being used for swimming again.
- Particularly during periods of heavy use it may be necessary to shock the pool weekly. This is because swimmers and children often take contaminants into the pool with them such as sunscreen, makeup, sweat and even urine (we all know what young children can be like). These can use up the normal free chlorine quickly so shocking restores the levels.
- If after you have tested your pool water it shows that the combined chlorine reading is high then you should take the opportunity to shock the pool to restore the levels.
- If your pool has turned green due to a build up of algae then the only way to resolve it, and make the water clear again, is to shock it.
Can you shock your pool with bleach?
It is possible to shock your pool using bleach but generally the chlorine levels in domestic bleach are relatively low at around 5% whereas liquid shock, for example, can be as high as 15%. You would therefore need much more bleach to achieve the same result.
It goes without saying, or at least it should, that if you do use bleach you should not use bleaches that contain fragrances or colors.
How soon after shocking your pool is it safe to swim?
Different types of shock can make a difference so the first advice would be to read the manufacturers instructions on the packaging which should tell you how long to leave it before swimming.
Ideally, after heavily shocking your pool, no-one should swim in the pool for a minimum of 6 hours and up to 24 hours.
You can test the water using test strips or an electronic water tester to establish when it is safe. The general consensus is that the free chlorine levels should be below 5 ppm and ideally below 3ppm.
You should leave the shock to work for at least 4 hours before you first test the water.
Swimming before these levels are reached can result in stinging eyes, skin irritations and potentially worse conditions such as lung irritation.
Can I put my solar cover on the pool after shocking?
You should not put the solar pool cover back on the pool immediately after shocking. High chlorine levels can degrade your pool cover quickly and they are too expensive to risk that. I normally leave mine off for at least 4 hours before I put it back on.