Reasons Why Your Pool Is Still Green After Shocking (And How to Fix It)

Written by Michael Dean
July 11, 2023

green swimming pool after pool shock

One of the most frustrating issues a pool owner faces is when clear blue pool water turns green overnight. A swimming pool can turn green for various reasons, most notably algae. The best thing to do in such a scenario is to act quickly and shock the pool. Unfortunately, occasionally, a pool may remain green even after the pool has been shocked.

Let’s look at possible reasons why your water might be green after shocking, how to fix it, and what you can do to prevent it from occurring again.

Main Takeaways

  • Pool water might be green after shocking for various reasons, such as metals in the water, algae growth, or using too much algaecide.
  • You can prevent your pool from turning green again by cleaning your pool filtration system or vacuuming the pool manually.
  • The pool filter needs to run for up to 24 hours after shocking.

Reasons Why Your Pool Is Still Green After Shocking 

Here are some main reasons your swimming pool may still be green after shocking it.

Weak Shock Treatment

You might have under-shocked the pool, the shock might have expired, or you may not be shocking correctly. The recommended dosage for shocking the pool is usually about 1 pound of shock per 10,000 gallons of water, but you may need to put in more shock depending on the severity of the algae infestation. You may need to use more shock or a stronger/fresher formula to kill the algae effectively. In some cases, you’ll need to double, triple, or even quadruple shock your pool when dealing with more persistent algae. You can over-shock your pool, though.

Be patient: sometimes, it can take several rounds of shock treatment to kill the algae and clear up the water thoroughly. So keep testing the water to see if the treatment is working. If the water remains green after a week, you may need to call in a professional to deal with the issue.

You should also ensure that you always shock your pool at night, as during the day, especially in strong sunshine, the UV rays break apart chlorine molecules, rendering your shock useless.

Poor Water Circulation

Your pool’s water circulation and filtering systems might not be functioning optimally. For the shock treatment to work effectively, it’s essential to have good circulation so that the shock is evenly distributed throughout the pool. Check your pool filters – they might need backwashing if they are dirty and full of debris or replacing if worn out. If the filter is still underperforming, have a professional do a maintenance and servicing check to ensure everything is running smoothly.

Incorrect Water Chemistry Levels

Pool shock treatment is most effective when the pH level of the water is between 7.2 and 7.6, but aim for it to be slightly on the lower level at around 7.2 and 7.4 for best results. If the pH level is too low or too high, the shock may not work as well, which may result in your pool remaining green after shocking the water.


If the swimming pool has high trace amounts of certain metals, such as copper, in the water, the water could immediately turn green after being shocked. This is because some metals oxidize after exposure to large amounts of chlorine. Test the water to check the metal levels in your water. If this is the issue, use a chelating agent or even a metal remover product to eradicate any traces of metal before attempting another shock.


Even though algaecide is supposed to prevent algae from taking root, overusing the chemical can cause harm. Some brands of algaecide are copper-based, which, as mentioned previously, can oxidize in the presence of chlorine and make the water turn green. To avoid this, don’t go above or below the recommended amounts of algaecide. Alternatively, use a metal-free algaecide.

Phosphate Overload

Too much phosphate in the water is not great. You should keep phosphate levels under 500 ppb (parts per billion). Algae thrive on phosphate, and the extra phosphate in your water can feed the algae, making it stronger and harder to get rid of.

How To Clear Your Green Pool

If shock and algaecide didn’t work, you could try using other remedies to clear a green pool.

Vacuum And Brush The Pool

If your filter is struggling to clear a green pool due to algae, jump in with a helping hand. Grab a pool brush and brush the pool surfaces in one direction. You can then vacuum the pool to help remove particles of the spores from your pool. Once the algae is removed from the pool surfaces, your filtration system should be able to do the rest of the work in cleaning and clearing your pool.

Baking Soda

Baking soda is another effective treatment to spot-treat a green pool. However, baking soda shouldn’t be used on its own for large algae infestations. Its active ingredient is sodium bicarbonate, which breaks algae up and makes it easy to scrub away. If your pool is in the correct pH range of 7.2 to 7.6, use around 1.5 lbs. of baking soda per 10,000 gallons of water. Keep in mind, however, that adding baking soda will raise alkalinity by about 10 ppm.

Arm & Hammer Baking Soda

Good old fashioned Arm & Hammer pure baking soda is a great option.

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Correct pH Imbalances

If your pH balance is off, test and correct it before shocking the water again. Test your pool once or twice a week and fix a chemical imbalance as soon as you spot it. Having properly balanced water can make a difference when shocking your pool.

Check Filtration System

Troubleshoot any issues your circulation and filtration system might be encountering, such as cleaning out your cartridges and replacing your pool pump impeller. Filtering and circulating your pool water after shocking is crucial to the shocking process, so ensure your system is working correctly for the best results.

How To Prevent Your Pool From Turning Green Again

Green pool water is undoubtedly a significant annoyance, but with the proper knowledge, you can prevent it from happening again. After all, the best way to clear your green pool after shocking is to prevent it from happening in the first place!

Get A Robotic Pool Cleaner

Getting a robotic pool cleaner might be expensive, but it is well worth it in the long run. Pool filtering and circulating 10,000-20,000 gallons of water is a major task, and to help keep your pump running smoothly, an automatic pool cleaner will go a long way in clearing out any elements that encourage a green pool to occur.

Invest In A Pool Cover

If you aren’t already using a pool cover, now’s a good time to buy one. Pool covers can make a major difference in keeping unwanted dirt and debris out of the water. As a plus, a pool cover can also help reduce the amount of evaporation and water loss, saving you money on water and chemical costs.

UV Light

Ultraviolet light is a more technical way of preventing an algae infestation. It is now easily possible to buy an ultraviolet pool sanitizer: UV rays disrupt the formation of single-cell DNA present in bacteria and algae, making it a deadly and efficient algae killer.

Insist On Proper Pool Hygiene

Private pool owners often overlook this aspect, but it is vital for swimmers to wear proper swimming gear and to shower before getting into the pool. Dirty swimsuits and unwashed skin and hair leave traces of all kinds of bacteria in the water. So make it a firm rule for yourself and anyone using the pool to rinse off before taking a dip.

Get My Free Pool Care Checklist

Download my free, printable pool maintenance checklist to help you accomplish regular pool care tasks for any type of swimming pool.

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How Long To Run The Filter After Shocking

I recommend running the filter for a minimum of 8 hours after shocking your pool to a maximum of 24-48 hours to allow the chemicals to circulate and work effectively. However, the exact length of time will depend on the size of your pool and the type of shock treatment being used. Not running the filter means uneven mixing of chlorine, resulting in a patchy and ineffective shock treatment, potential damage to pool equipment, and algae remaining unfiltered and still present in the pool.

Questions? Let me know!

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