How To Shock A Swimming Pool

What is shocking a swimming pool, and how do I do it!?

  1. Sanitise your pool with a heavy treatment of Chlorine, either granular or liquid. Ensure that non stabilised chlorine is used.
  2. Lower your pH with Hydrochloric Acid, by doing this chlorine will be more effective.
  3. Ensure then system is on and running for a 24 hour period to disperse the shock treatment around the pool and clean the filter for any debris captured.
  4. Test and re balance 2 - 3 days after and make any additional adjustments required and switch the filtration system back onto its normal operating procedure.


There are 3 different stages of algae in which different amounts of pool shocking are needed -

  • Light green algae
  • Dark green algae
  • Black green algae


These are not different types of algae, it’s just different amounts. The more algae in your pool water, the darker the green colour will be. I’ve seen pools almost black with an algae infestation. Gross!

Light Green Pool Water

If you have a light green pool you need to shock your pool in order to kill algae (add more Acid and Chlorine than usual). 

Algae feeds off high pH and your chlorine isn't as effective when your pH is high, you need to lower your pH using hydrochloric acid. 1-2L of it to start with. Be careful when adding it to make sure it doesn't splash up on you as it is highly toxic and dangerous, and only add 1L every 24 hours if your pool is Vinyl lined as it's more sensitive to harsh chemicals.

You also need to shock your pool with chlorine, 2 cups/400 grams of granulated chlorine (not stabilized) or 3 tubs of 15L chlorine (as it's actually only 20% chlorine and the rest is water), or if your pool is salt water chlorinated adding 2-4 bags of salt (once again you should get your salt tested at your local pool shop to see exactly where it's sitting) and turning your chlorinator to 100% for a couple of days to really boost that chlorine and get that water sanitized. Your salt should be sitting at around 5000ppm (parts per million) and each 20kg bag of salt equates to 500ppm.

If you've added your salt and turned your chlorinator up to 100% but after a few days theres still no or next to no chlorine being produced or your "low salt" light is still on even though you know there's plenty of salt in there, your electrode may need replacing. An average life span for an electrode is 3-5 years. You also will need to clean your cartridge filter or back wash your sand filter, and ensure all of your skimmer baskets and pump baskets are empty.

If the green in your water has set up home on your pool steps and doesn't want to move out (sounds like my mid-twenties children) adding hydrochloric acid should slowly start killing the algae on your steps as well, if your pool is concrete you can use a metal brush or if your pool is vinyl you can use a normal plastic bristle brush to help brush this algae off.

Mr Pool Man can't sell or ship Hydrochloric Acid, Liquid Chlorine, Granulated Chlorine or Salt online as it's either dangerous materials or too heavy, though you can grab them from your local pool shop.

We recommend testing your water a few days after this heavy dose to check your levels. You can do this yourself using a 7 in 1 Test Strip Kit.

Once your pool is sparkling, don't forget to add 500g-1Kg of Stabilizer/Cyanuric Acid/UV Blockout to keep that chlorine in the pool and not being sucked up by the sun. Adding 500g of Stabilizer once a month should keep this in check.

Dark Green Pool Water

You're looking at following the above steps but at a slightly higher dose of Acid and Chlorine. For example adding 2-3 Litres of acid over a space of 48 hours and adding 2-3 cups/600g of granulated chlorine. Also, darker green water may also be a cause of stagnent debris sitting on the bottom of the pool which needs to be cleaned out before you dose it. Be sure that this is all scooped up using a leaf shovel, followed by being manually vacuumed out of the pool using a vacuum head, appropriate length hose for your pool (9m11m or 15m) and a telepole.

SEE ALSO: How to manually vacuum your pool

Black Green Pool Water

If you have a black green pool, you will be looking at doing the "Light Green Pool Water" dosage as outlined above x3. This may take some filtering, cleaning or backwashing of the filter, and more filtering to completely clean up over a period of 2-3 weeks. Black green pool water will almost certainly have stagnant debris sitting on the bottom of the pool which needs to be cleaned out before you dose it. Whether it be leaves or a creature that got stuck and never made it out, be sure that this is all scooped up using a leaf shovel, followed by being manually vacuumed out of the pool using a vacuum head, appropriate length hose for your pool (9m, 11m or 15m) and a telepole.

Note: If you have a vinyl liner pool, diluting any chemicals that are being added to your pool in SEPARATE tubs of water (we don't want any chemical reactions here) is always a good idea to ensure no damage is done to your liner.

Please see a list of other useful pool blogs below:

Note: This blog is a rough indication of advice for an average sized pool and average dosing recommendations. Mr Pool Man always recommends getting your water tested by a pool professional before adding any type of chemicals for your own safety, or giving us a call on 1300 511 901 or contacting us if you are unsure. Mr Pool Man does not take any responsibility for incorrect dosages

Post author:

Tom Hintze

Head of eCommerce & Operations at Mr Pool Man,
Co-Founder at Water TechniX


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