Shocking a pool is a maintenance practice that keeps your pool clean and inviting. Also known as “super chlorination”, shocking can be done periodically to sanitize the pool and maintain an adequate free chlorine (FC) level, usually if the FC is stubbornly low for a while. However, it’s more often done when an issue occurs in the pool, such as an algae outbreak. Shocking is done to super-chlorinate the pool water, killing all living organisms and making the pool safe for humans once again.
If you think you need to shock your pool but aren’t quite sure where to start, you’re in the right place. Here’s your complete guide to how to shock a pool, whether it’s made from fibreglass or another material.
How to shock your pool
Before you get into the actual pool shocking process, be sure to first follow these steps to prepare.
Pool shock prep
Here’s what you’ll need to prepare for pool shocking:
- A large (5 gallon) bucket
- Pool shock
- Rubber gloves
- Safety goggles
- A stirring stick
- Old clothes that you don’t mind getting bleached
Follow these pre-shock steps:
- Check and adjust pH levels until they’re at 7.2 to 7.4. This will allow your chlorine to work most efficiently.
- Clean the pool and remove the pool cleaner.
- Run your pool pump.
- Calculate your pool volume.
- Determine how much shock is needed to fix the situation. This can depend on whether you have an algae problem or are just doing general maintenance. If general maintenance, add 10 times the current combined chlorine (CC) level as available chlorine. For example, if you have a CC level of 2 ppm, you should add 20 ppm worth of available chlorine.
To calculate your CC level, use a pool test kit or strips. They should give your FC and total chlorine (TC) levels. From there, determine your current CC level by subtracting FC from TC. CC is the difference between the two:
CC = TC – FC
- If you’re shocking your pool for algae, the rule of thumb is based on your pool water’s colour, which changes depending on the type of algae problem you have:
- Teal green. Usually caused by green algae (the most common type). Plenty of double-shocking your pool and brushing will help remove the dead algae.
- Dark green. This algae is mustard or yellow-green in colour. Generally, on top of triple-shocking your pool, you will need a specialized algae remover.
- Black green. This is a serious infestation of black algae and the hardest type to kill. You can identify it by dark black-green spots on your pool walls and floor. It requires extensive (quadruple) shocking, brushing and specialized algaecide for an extended period.
Shocking your pool
Now that you’ve prepared, follow these steps to shock your pool.
- Get your gloves and goggles on.
- Pre-dissolve the shock in the bucket of water – it’s best to do so to avoid bleaching and discolouring the pool surface.
- Fill the bucket with water
- Add shock
- Stir with a stirring stick
- Add shock directly to the pool, according to product label instructions.
- Add shock when the sun is not shining directly on the pool. Nighttime shocking is usually best.
- Brush the walls and floor to help distribute and circulate the shock throughout your pool.
- Leave the pool pump on overnight (or for at least 8 hours).
- Check the chlorine levels before swimming. For most chlorine shocks, you’ll need to wait at least 12–24 hours. Be sure your FC levels are at 3 ppm before you go swimming.
Why shock your pool
There are several reasons to shock your pool. For one, it reduces the buildup of microcontaminants and organic matter. Shocking also destroys both harmless and pathogenic bacteria in the water and kills algae blooms or treats cloudy pool water.
On top of this, taking good care of your pool extends its life – which is very important considering the large investment you’re making!
Finally, shocking your pool will remove CC molecules (chloramines) that irritate your skin, eyes and respiratory system. By shocking your pool, you’re adding enough chlorine or other chemicals to clean the water and destroy the buildup of chloramines.
The ABCs of shocking pool water
Here are the three reasons to shock your pool, also known as the ABCs of shocking:
Algae
It’s important to NEVER swim in a pool affected by algae, as it can be very harmful. The good news is you can shock your pool to kill algae – while algaecide prevents algae growth, shocking kills any current algae growth you may have.
Bacteria
Use chlorine shock to kill bacteria after unwanted natural events (like severe storms, heavy rain or long winters with no use) or swimmer events (like accidents or spills) that may bring bacteria into the pool.
Bather waste includes any contaminants brought into the pool by swimmers, including dead skin cells, hair, lotions, cosmetics and soaps, as well as more potent contaminants like sweat, fungus and, yes, even urine and feces.
Cloudy water, contaminants and chloramines
Red-eye or a strong chlorine odour is caused by chloramines. Cloudy pool water is often a symptom of poor water imbalance and low sanitiser levels.
When chloramine levels exceed 0.3 ppm, add enough chlorine or non-chlorine shock to break apart the CC molecules. Chlorine becomes CC when it bonds to nitrogen or ammonia in the water. This bond makes the chlorine molecule useless and causes the pool water to smell strongly of chlorine. These chloramines can irritate swimmers’ eyes and skin, and make for a generally unpleasant swimming experience.
When to shock your pool
There are several scenarios when it’s a good idea to shock your pool. For good maintenance and to avoid big issues, it should be done both on a weekly basis and:
- When the water is cloudy
- After heavy use
- If you notice algae growth – whether it’s green, yellow or (especially) black
- If there are unwanted bacteria present from toilet accidents, lotions, sunscreen, etc.
- After heavy weather like rain, storms or extended heat and sunshine
It’s best to shock your pool after direct sunlight has passed over it, as the chemicals used can break down in direct sunlight. For this reason, many people shock their pool in the late afternoon since there’s still enough sunlight to get the job done, and no one wants to swim just before dinner.
Frequently asked questions
This guide should answer most of your burning questions about shocking your pool, but if you’re still curious about something, check out these frequently asked questions.
Can saltwater pools be shocked?
Yes, saltwater pools can be shocked. Although it’s thought that they can’t or shouldn’t be shocked, it is certainly possible.
Is powdered shock or liquid shock better?
Liquid shock is generally a safer option than powdered shock. However, if added to a pool correctly, powdered shock will not cause any damage.
Can I use something other than shock?
There are alternate products to shock on the market that aren’t chlorinated.
Should I add the shock to my filter/skimmer?
Never add shock to your pool filter or skimmer, as it can ruin them.