You need to raise the level of your chlorine – shock the pool – and maintain that high level until all the algae is dead. This may take 3 to 4 days.
Keep your pump and filter running. Give the shock a good 12 to 24 hours to work it's magic. If the algae hasn't cleared up after 24-48 hours, clean and brush the pool and add another shock treatment.
You will need to quadruple shock your pool by added 4 pounds of shock to every 10,000 gallons of water.
Shock Your Pool with Chlorine to Kill Algae
This is the main event in clearing a green pool—killing the algae. Pool shock contains a high level of chlorine that will kill the algae and sanitize the pool. For the best results, use a shock that contains at least 70% available chlorine (calcium hypochlorite).
You cannot overshock a swimming pool or add too much. Adding too much shock or overshocking your pool will kill off algae. The negative of adding too much shock is it will upset the chemical balance of your pool.
If the pool is still very cloudy or green, you may need to shock it to make it safe to swim in again. First, make sure that the filter system is working properly and the chemicals are still at the proper levels. Next, mix up your chlorine shock (hyperchlorinate) treatment.
A pool filter should be run for a minimum of 6 hours after shocking a swimming pool. This is to allow the filter to clean the water and give the shock enough time to fully mix with the pool water. Running the filter after shocking for 24 hours to 7 days is necessary if the pool has a large amount of algae.
When the levels are properly balanced, chlorine will keep the algae at bay, but the water will slowly begin to turn green as the algae take over if there's not enough. But be careful—adding too much chlorine in pool water can cause those metals to oxidize and turn the pool a different shade of green.
Although, if you overdo the shock treatment, you risk getting green hair from chlorine due to the excess chlorine oxidizing the copper in the water. You can execute a shock treatment with a few different types of pool shock, just be mindful of how much you're using.
Pools can immediately turn green after shocking when they have metals like copper in the water. These metals oxidise when exposed to high levels of chlorine which makes the pool water turn green. Adding a metal control product such as Zodiac Metal Remover will help to restore the pool water.
Algaecide should be used after each shock treatment, so it has a better chance to support your chlorine as it works its magic. Be sure to shock your pool first, then when the chlorine levels of your pool return to normal, add the correct amount of algaecide to several places around your pool while your pump is running.
After Shocking Your Pool
It is safe to swim once your chlorine levels are around 5 ppm or after 24 hours. It is always best to test first!
Never close the cover immediately after shocking the pool. It is recommended to wait several hours before closing the cover. Use a test kit to regularly test the pool water. If the tests results are good, this does not imply the water chemistry was good prior to your current test results.
When the chlorine has completely finished working, the algae in the pool will turn a white/gray color and will either settle to the bottom of the pool or be suspended in the water. There shouldn't be any more green color and the water visibility should be improving. Run the filter 24/7 and backwash as needed.
It's not a good idea to use pool shock at the same time as clarifier. Some clarifiers are polymer based and the shock can act to break up the polymer causing the clarifier to be ineffective. It's best to shock your pool before and wait a day or two before adding clarifier.
In theory, if you have a cloudy swimming pool, you can add chlorine to “shock it” and clear things up. Chlorine will get the job done. But, the amounts may vary and you may have to really pound the pool with chlorine to get the water totally clear.
Pool water turns green because of algae in the water. Algae can grow rapidly, particularly when it's warm like Summer, which is why it can surprise you overnight. This generally comes down to an imbalance or lack of chlorine in the water.
It's pretty tough to over-shock your pool; shocking your pool two days in a row with the proper dosage for your pool volume shouldn't be a problem – and in fact, is sometimes even needed to rid your pool of algae and other contaminants.
There are a few different types of algaecides that contain various chemicals to suppress and fight off algae. Many of them include copper or copper sulfate. It's this copper that oxidizes in the water. And when copper oxidizes it turns a green color causing your pool to look green.
Baking Soda and Green, Blue, or Yellow Algae
You'll need to use an algaecide to kill the algae and superchlorinate your pool to clear the water. After this treatment, test your pH and alkalinity and add baking soda to raise alkalinity to at least 100 ppm and pH to between 7.2 and 7.8.
Green pool water is often caused by the presence of algae in your pool. Algae blooms can appear when your pool has a low Free Chlorine. Exposure to high heat, heavy rain or poor circulation, without the use of a preventative algaecide, also increase your risk of developing pool algae.