Pool Is Green But Chlorine Is High

You may be wondering why your pool turned green even when you are sure that the chlorine level is high. Well, it’s not a strange occurrence as it happens once in a while.

Sometimes, you will go to bed fully aware that your pool is clean and clear, but wake up to a very cloudy or green pool. Occasionally, this happens to most pool owners. 

If you are noticing something like that for the first time, you don’t need to panic. It’s a minor issue that can be resolved immediately.

Understanding the possible causes of your pool turning green when chlorine is high will help you to know the right way to tackle the problem. Below are the most common factors that can make a pool turn green, even when the chlorine is high:

Dissolved metals: when the chlorine level in your pool is high, it can react with dissolved metals in the water Chlorine can also react with the metal surfaces to release unwanted compounds into the pool.

As the metal elements in the pool increase, the color of the water changes.

High level of pH: if the pH level in your pool is high, the sanitizer may not be able to function properly. So, you have to be sure that the chlorine sanitizer is functioning properly. 

Test the pool first to know if the pH is within the recommended range of 7.2 – 7.8. If it’s above 7.8, correct it first and check whether the issue will resolve with time.

Low free chlorine: the free chlorine in your pool may be low, irrespective of the amount of total chlorine you have in your pool. If that’s the case, then the amount of combined chlorine in your pool is very high.

Free chlorine, not combined chlorine, kills bacteria and algae in the pool. Combined chlorine is chlorine that has reacted with other compounds to form chlorine compounds. 

With this issue, you need to shock your pool as soon as possible.

Pool filter: most likely, your filter system is faulty or you don’t use it as you should. Your pool’s filter helps to remove debris and algae from your pool.

Even when you shock your pool, you need the filter to completely clear it. Without the filter, dead algae and other microbes will accumulate in your pool.

So, you need to make sure that the pool filter is working properly, and at least eight hours a day.

How do you fix a high chlorine pool that is green?

First, you need to know the root cause of the problem. As we discussed above, knowing the cause of the problem will help you determine the best solution for it.

If the root cause is imbalanced pH levels, then you need to adjust the pH level before taking further steps. A high pH level affects the effectiveness of the chlorine sanitizer.

So, even if the chlorine level is high, it may not be effective enough to kill the algae in the pool. Click here to learn more on how to lower pH in your pool naturally.

The presence of metal elements like copper could be the culprit. If the copper plumbing starts to leach into the pool, the water is likely to turn green after the shock. 

When the chlorine shock reacts with the copper, it forms metal compounds that turn the pool green.

To solve this problem, you need chelating compounds. The chemicals can easily help you remove copper from the water. You can get them in pool stores.

Low free chlorine in the pool water can also be the cause of green pools. As we discussed above, you may have a high amount of chlorine in your pool, but the free chlorine present is low. 

This means that higher percentages of the chlorine in your pool have reacted with other compounds and are no longer effective. The reacted chlorine is known as “combined chlorine.”

With a high level of combined chlorine, you need to shock the pool. The amount of combined chlorine in your pool should not be higher than 0.2 ppm. Shocking your pool is the best solution for this.

A low pH level can affect the water chemistry in your pool. When the pH of your pool water becomes low, it can cause metals like copper to dissolve in the water. 

As we know, these metals can react with chlorine to form compounds that make the water green.

To solve the problem, we need to balance the water chemistry by adjusting the pH level. The recommended range is 7.2-7.8.

Let’s not forget pollen from flowering plants either. If you have flowering plants close to your pool, you need to cover your pool to prevent these substances from entering the pool.

Even if you don’t have flowers, your neighbors may have them, and the pollen can travel a long distance in the air. So cover your pool to avoid them.

They can make your pool turn green. If you have a high accumulation of pollen in your pool, you can use flocculants and skimmers to remove it.

A high level of stabilizer can cause chlorine lock. Cyanuric acid is used to prolong the lifespan of chlorine sanitizers. It protects the sanitizer from the UV rays of the sun. 

The ideal amount of stabilizer your pool needs is 50 ppm. If the stabilizer becomes too high, it can lock the chlorine molecules and render them ineffective. 

To solve the problem, you need to dilute the water in your pool to lower the concentration.

You also need to check your filter. If you are not filtering as required, or if your filter system is not working properly, debris and dead algae will accumulate in the pool.

Some of the debris can be greenish, which will turn your pool green and cloudy, even though the chlorine level is high.

Can algae grow in a pool with high chlorine?

Yes, algae can grow in a pool with high chlorine if the free chlorine present is low.

So, you may have high chlorine in your pool, but the level of combined chlorine is also high. If that is the case, the chlorine in your pool is not effective and algae can thrive in such an environment.

What you need to kill algae in your pool is free chlorine. If free chlorine reacts with other compounds like ammonia, it becomes ineffective.

Though the chlorine that reacted with the ammonia is still present in the water, it can no longer kill algae or bacteria effectively.

This means that the total chlorine present in your pool doesn’t determine the effectiveness of the chlorine. The amount of free chlorine present is what determines how effective the chlorine is.

The recommended range of free chlorine in a pool is 2 ppm to 3 ppm.

How much chlorine does it take to clear a green pool?

The amount of chlorine shock you need depends on the volume of your pool, the amount of combined chlorine, and the amount of algae in the pool.

If the pool is infested with a lot of algae, you may need to double shock the pool.

But, first, you have to find out the amount of combined chlorine present and the required chlorine change to break it up.

So, you need a DPD kit to determine the free chlorine and total chlorine. You can use the instructions below to determine the amount of chlorine shock you need to clear your green pool.

First, you need to measure the amount of free chlorine in the pool with a DPD kit. You can get the kit online or from pool stores.

To do that, you have to fill the DPD test tube by dipping it into the pool water to about 1.5 m depth. Ensure it reaches the tube’s fill line.

Add one free chlorine tablet and cover the tube with the lid. (Note that some kits use chlorine drops instead of tablets.) Shake until the chlorine tablet dissolves.

Compare the color of the water in the tube against the chart on the kit. Record the reading.

In the same manner, use a total chlorine tablet to find the amount of total chlorine present in the pool. Fill the test tube with water, add the total chlorine tablet, and shake until it dissolves. Measure the color against the chart and record the reading.

Then use the values to calculate the combined chlorine. The combined chlorine is the chlorine that has reacted with other compounds like ammonia.

Combined chlorine = total chlorine – free chlorine.

For example, if the total chlorine and free chlorine measured are 3.5 ppm and 1.5 ppm, respectively, the combined chlorine will be:

Combined chlorine = 3.5 – 1.5 = 2 ppm.

Remember, the combined chlorine shouldn’t be more than 0.2 ppm.

The next step is to find the breakpoint, which is the amount of chlorine needed to break the combined chlorine (compound) in the pool. You do this by multiplying the combined chlorine by 10.

Breakpoint = Combined chlorine x 10

Since the combined chlorine from our calculation is 2 ppm, the breakpoint will be:

Breakpoint = 2 x 10 = 20.

Remember, we already have some free chlorine in the pool water. So to find the actual amount to add to the pool, you need to subtract the free chlorine from the breakpoint.

Thus, the actual amount of chlorine change is:

Breakpoint-Free Chlorine = 20-1.5 = 8.5 ppm.

On the package of the chemical, you will usually see the amount of shock required to raise the chlorine level by 1 ppm for every 10,000 gallons.

So, we are using 10,000 gallons as the standard for our calculation. 

Divide your pool volume by 10,000.

Assuming your pool volume is 30,000 gallons, you will have:

30000/10000 = 3

Then check the pack to know the correct amount of shock needed to raise the chlorine by 1 ppm.

Multiply the amount on the pack by the pool volume calculated and the actual amount of chlorine change.

Assuming it is written on the pack that you need 2.5 ounces to raise the amount by 1. From our own calculations so far, we will have:

2.5 x 3 x 8.5 = 63.75 ounces.

That means that you need to add 63.75 ounces of chlorine shock to the pool to break up the combined chlorine.

Remember, these figures are assumed figures. You need to do the test to determine the exact figures for your own pool.

The figures above are for a normal shock. Most of the time, the value may not be enough to clear a pool and still maintain the chlorine level. To take care of that, you may need to double shock the pool.

Will shock clear a green pool?

Yes, you can use chlorine shock to clear a green pool if algae is the cause. Pool shock helps you kill the algae in your pool water

So, once you kill the algae and filter them out, the pool will be clear again.

However, other factors may be responsible for the greenish color of your pool. If it’s an issue of dissolved metals, pollen, filtration system, or pH level, pool shock cannot be used to clear the green pool.

How do you clear up a green pool fast?

As we discussed in this article, pool shock is not enough to clear a green pool. If you want to clear up your green pool fast, you need to scrub and vacuum clean the pool first before adding the shock.

This method helps to reduce the amount of work the shock will do.

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