Pool turned green after shocking- University Study Explains

Pool shocking is meant to reduce contaminants in your swimming pool such as algae, chloramines, and bacteria, to make your pool safe. However, the process is not always smooth, and you may find yourself in a situation where your pool turns green after shocking.

Whether you are a new swimming pool owner or a seasoned one, your pool turning green after shocking is a signal that something is wrong with either the shocking process or your pool, and you need to address the problem as soon as possible.

But why do pools turn green after shocking? Pools turn green after shocking because there are still phosphates in the pool water. Phosphates are a nutrient for algae. Phosphates will first decrease the chlorine level, and then algae have the perfect environment to grow, causing your pool to turn green.

According to the University of Alberta, a study concluded that the algae in lakes is reduced when the phosphates are reduced. It is the same scenario in a pool, reduce the phosphates so that the green color caused by algae is lowered.

Here is a video that explains how to dissolve your pool shock before adding to your pool:

Can too much shock turn pool green?

To answer the question of whether too much shock of your pool can turn it green, we need to first look at what pool shocking entails and why the water turns green.

What is pool shocking?

To shock a pool, you need to add chlorine into a pool. This increases the level of free chlorine. Free chlorine is needed to kill off bacteria, chloramines, and algae.

There are many factors that determine the frequency you are required to shock your pool, such as the number of people using your pool, the level of your free chlorine levels, algae in your pool and a high combined chlorine level of above 0.5. Ideally, you are required to do shocking at least once a week if your pool is extensively used by many people or done in correlation to weather conditions, such as whether the weather is consistently sunny or rainy.

What causes the pool to turn green after shocking?

There are several reasons why your pool can turn green after shocking. Some of these reasons include:

  1. Heavy metal in the pool. Chances are your swimming pool water has been contaminated with heavy metals. This mostly happens when you change your water supplier or water source. The only way to determine if your pool is turning green due to heavy metal is by testing the water through a specialist or taking a sample of your pool water to your local pool shop for testing.
  2. Low pH combined with metal plumbing. This mostly happens when you are using in-house water for your pool. The problems start to arise when this water starts corroding your pipes, introducing foreign materials in your pool, resulting in contamination. After shocking, the heavy metals released in your pool react with chlorine to form the green substance you see in your pool.
  3. Copper-based algaecides. This happens mainly because copper-based algaecides were used in the past for your pool. While copper-based algaecides prevent the growth of algae, when used in excess, it can lead to elevated levels of copper, which react to chlorine introduced in your pool during the pool, shocking to form green water.

Other factors such as not using a vacuum to clean your pool, failing to brush it regularly and using unrecommended methods of shocking can also result in your pool turning green after shocking.

Can too much chlorine turn pool water green?

The main reason for pool shocking is raising “free chlorine” levels in your swimming pool to a point where contaminants such as algae, chloramines and bacteria are destroyed.

Therefore, every pool owner knows the significant role chlorine plays in keeping their swimming pools clean. However, the problem of how much chlorine is needed before your pool turns green or becomes toxic continues to divide professionals and, in this section, we are going to explore everything you need to know about chlorine and the role it plays in pool shocking.

For starters, you are required to shock your pool when:

  • Algae begin to grow in your pool
  • The level of free chlorine on your pool measures zero
  • The combined chlorine level rises above 0.5 parts per million (PPM)

Therefore, three of the top three reasons that call for shocking your pool involve chlorine levels and how you need to keep a balance of their levels for your safety and the pool’s hygiene.

To effectively shock your pool using chlorine and non-chlorine chemicals, you also need to know the four types of chlorine you need to test and keep levels before, during and after shocking:

  1. Free Chlorine (FC): This is the amount of chlorine that is already in your pool disinfecting water. The free chlorine levels on your pools are supposed to be between 1 and 3 ppm.
  2. Combined Chlorine (CC): This is the chlorine that has already been used by your pool. The levels for CC are supposed to be 0.2 ppm.
  3. Total Chlorine (TC): This is the sum of CC and FC.
  4. Breakpoint Chlorination: This describes a point where breakpoint chlorination has been reached and the free chlorine in your pool starts to build up and sanitize your pool.

Therefore, failing to account for the levels of FC, CC, TC and breakpoint chlorination can lead to too much chlorine in your pool which can result in your pool turning green due to a high concentration of chlorine. Therefore, you should be careful about the levels of chlorine you use in your pool.

How long does it take for a green pool to clear after shock?

Sometimes you may find yourself in a situation where you have shocked your green pool, but after hours and sometimes days of waiting, the green color is yet to disappear. This may be caused by a number of reasons, including:

  1. Algae are still not dead: After shocking your green pool due to algae, you have to patent because the algae don’t die immediately and can take hours and sometimes days before they are all gone.
  2. Too much chlorine when shocking. This is also a major problem that many pool owners make when shocking. Adding a lot of chlorine does not necessarily mean that your pool will be cleaner. When done in excess, it can lead to your pool turning or remaining green because the excess chlorine oxidizes copper in the water, turning it green.
  3. Failing to brush your pool thoroughly. Your pool walls may still have pollen, bacteria, algae, and organic debris that you failed to brush before adding water. This means that, no matter how much pool shocking you do, the result will always be green or may take a long time to clear.
  4. Failing to use pool Floc or clarifier when doing pool shocking. These two chemicals are almost similar in usage and using one of them will help you clear the cloudy green water fast.

Realistically, you shouldn’t expect your pool to clear immediately after shocking, and sometimes, the process can take up to four days before all the cloudy green water clears up.

Algae on bottom of the pool after shocking

Pool algae is a result of low chlorine levels in your pool, poor water chemistry, or bad filtration. Algae can also be introduced in your pool through swimwear and toys used in your pool.

To understand why your pool may still have algae after shocking, you need to know about the different types of algae, and depending on the color of the algae, you will be able to remove them:

  1. Green pool algae: These types of algae are the most common and the easiest to remove. They float on your pool and are green in color. The algae can be removed by using a vacuum and brushing your pool.
  2. Yellow pool algae: They are very rare and are mostly found in humid climate conditions. They mostly cling to the shady corners of your pool. To remove these types of algae, you need to brush your pool thoroughly and then run another shock to your pool water. These algae are also chlorine resistant; hence you should make sure that you only use non-chlorine chemicals during shocking.
  3. Black Pool algae: The black pool algae is a bacterium; therefore, it is not easily killed. To clean the algae, you will need multiple rounds of deep cleaning. The algae also grows back if your pool is not thoroughly cleaned.

Therefore, the reason why your pool may still have algae, even after doing multiple pool shocks, is that the chemical treatment of your pool is ineffective to the algae you are trying to get rid of. Therefore, the solution to your algae problem should be combining your shocking strategy with other methods such as wall scrubbing and vacuuming to remove remnants of algae and bacteria that the pool shock did not remove.

Why is my pool still cloudy after shocking it?

You have finally decided to shock your pool after weeks of cloudy green water. However, after multiple pool stockings, the cloudy water is still persistent. This may be caused by several reasons, including:

  1. Chemicals used to shock your pool can cause cloudy water. This happens when the chemicals alter the alkalinity of your pool. High chlorine levels are also not good for your pool and can cause cloudy water on your pool.
  2. You may be having filter problems: Shocking your pool is sometimes never enough and you need to combine it with other methods such as water filtering to clear your water. In most cases, it doesn’t matter how much you shock your pool, if you do not filter it, the cloudy water will persist.
  3. High levels of cyanuric acid; Also referred to as Cya or stabilizer, is a chemical used for protecting pools from losing chlorine during shocking. Too much cyanuric acid can cause cloudy water after shocking your pool; hence it should be less than 50 ppm.
  4. High levels of calcium: hard water, by default, is scummy. Too much calcium in the water, which results in hard water, can cause your pool to have cloudy water and shocking your pool will not remove the scum in your water.
  5. Algae concentration in your pool: Shocking the pool failed to eliminate all algae, resulting in your water staying green. You should also note that algae such as black pool algae and yellow pool algae are hard to kill using shocking alone, leaving your pool cloudy even after thoroughly shocking it.
  6. The chemical reaction between copper and chlorine. Chlorine oxidizes copper, turning the water green during shocking.

What tactics did actual pool owners try to eliminate the green in their pools:

Tactics Used by Pool OwnersPercentage of total results
Some pool owners used new cartridges in their pool filter, it did not work well to remove the algae2
Pool owners have tried algaecides. They will kill present algae, but they did prevent more algae from entering the pool environment since algae enter via the wind, or even contaminated swimsuits.9
Chlorine through shocking, but you need to appear to maintain a high enough level of chloride to continue to kill algae. I recommend the HTH 52023 Super Shock Treatment. Click here to purchase it on Amazon.40
Shocking the pool and then adding a phosphate remover (click here to view a natural phosphate remover on Amazon). This seems to have worked for the long term in pools33
Treating the pool for metals such as copper or iron with sequestrant. It was done before shocking the pool. Seems to be with owners that use well water or that have city water that is hard in general. 12
Some claim that all that you need to do is increase the pH level to above 7, but I do not see how this will provide algae growth. 4
data derived from various swimming pool owners

How to fix cloudy green pool water

Cloudy green water is a problem for many swimming pool owners, and in some cases, fixing it is a harder job than draining the pool.

However, in cases where the cloudy green water is fixable, you should consider applying any of these tips to your pool:

  1. Ensure your pool’s filters are working properly. You should also ensure that it is clean to prevent the filter from being the source of cloudy green water.
  2. Shock the pool and add algaecide or yellow out, depending on the color of your algae. As a pool owner, you should know that applying chlorine chemicals alone while shocking will not kill all algae, and you need other specialized chemicals that help in killing algae.
  3. Vacuum your pool to waste. This is to prevent future problems with dirt and algae that might remain, even after a thorough wash.
  4. Thoroughly wash the walls of your pool. This is best done by using an algae brush. The goal of this wash is to ensure that there are no more algae in your pool. Also, this step should not come before vacuuming because the goal is to kill and remove algae in your pool. If you start with vacuuming your pool and then thoroughly washing it, a good chunk of washed algae will remain in your pool and may sprout in the future.
  5. Shock your pool with chlorine. This will help you kill algae in your pool and sanitize it. The best way to approach shocking is by using a shock that contains 70 percent chlorine.

After getting rid of algae from your pool, it is important to keep it that way. This can be done by maintaining proper sanitization levels. This can be done by regularly testing your water frequently.

Aron Blake

I am the lead copywriter on Homezesty and the Webmaster. I have a lot of experience in home renovations and the creation of style. I enjoy writing and sharing my tips on how to create the best living environment. My Linkedin Profile, My Twitter Account

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