How to Clear a Green Pool FAST


Why Is My Pool Green?

So what causes a green pool?

The number one cause of green pool algae is a lack of sanitizing agent in the water, and chlorine is the most effective sanitizer for treating this condition.

If you have a green pool, you likely have little to no chlorine in your water. Maintaining a proper chlorine level is the key to keeping a crystal clear pool.

The solution is to bring your chlorine level up to the shock level, and maintain it at that level until the algae are extinct.

To measure Free Chlorine (FC) at a high shock level. I recommend using the FAS-DPD test kit to measure FC at a high shock level.

Additionally, you will need a telescopic pole, net, rush, and vacuum.

There are broadly six steps for clearing up your green pool.

Clean Up Your Pool

As a very first step, you will need to clean up your pool debris. Organic materials consume chlorine, so you want to remove them as much as you can, so you don’t have to use as much chlorine down the road. 

Depending on the size of your pool, this step can take quite a bit of your time.

If your pool is extremely dirty, then it’s a good idea to vacuum the waste to prevent your filter from clogging up.

Test the pH and Chemical Levels of Your Pool

Next, you will test the pH.

You’ll want to first test the pH of your pool before you pour chlorine into it. Otherwise, your pH readings won’t be accurate. 

The ideal pH range is between 7.5 to 7.8. You will want to treat your pool with muriatic acid If the pH is above 7.8.

On the contrary, you will want to use a soda ash If your pool pH is below 7.5.

Afterward, test the cyanuric acid level in your pool, also known as CYA or stabilizer.

Both CYA and chlorine have essential roles in keeping your pool healthy.

The sun eats up chlorine, and what CYA does is it essentially acts as a sunscreen for your chlorine.

If the cyanuric acid level is too low, the sun will quickly consume chlorine. 

On the other hand, if the CYA level is too high, the chlorine will be less effective.

Generally speaking, you want to keep the level of CYA at around 30-60 ppm for non-salt water pools. If you have a salt water pool, then that number should be around 70-80 ppm.

If your CYA is either above or below the recommended level, you’ll want to use the pool math calculator to figure out how much you will need to add or remove from your pool.

You want to take extra precaution when using cyanuric acid since it can’t be broken down like chlorine. The only way to eliminate it is by draining water and adding back fresh water.

You can test your free chlorine level if your CYA is at an optimal level. As mentioned above, you’ll need the FAS-DPD test kit to measure how much chlorine you will need to shock the pool.

In case your pool is dark green, your pool will likely have a reading of zero parts per million free chlorine

Determine The Shock Level for Your Pool

Next, you will need to refer to the CYA chart to determine the shock level you will use to slam your pool.


Using the chart, you can match the free chlorine shock level with the CYA level.

Suppose your pool has a CYA level of 50, the chart shows that you will need a shock level of 20 ppm for your free chlorine.

Then, use the pool math calculator to determine how much chlorine you will need to reach the shock level. 

Add Chlorine Into Your Pool

Then it’s time to put chlorine into your pool.

I need to emphasize that when you shock your pool, you need to make sure you leave your pump running 24/7 to ensure proper circulation and filtration of the water.

Your efforts will be useless if you shock your pool once and call it since the important part is maintaining shock level.

This part is important because chlorine is continually eaten away by organic material and the sun, so It’s crucial to sustain the shock level so the algae won’t bounce back.

Maintain The Shock Level for Your Pool

It’s a good idea to test the free chlorine level every few hours in the beginning. You want to then continue to add the needed amount to maintain the shock level.

The chlorine will start to decline at a slower rate as more algae dies off, and you won’t need to check the chlorine level so frequently. 

It’s just a matter of waiting after you have sufficient levels of chlorine in your pool to maintain shock level.

Also, don’t forget to clean your filter daily to remove dead algae that is picked up by your filtration.

Continue to vacuum your floor daily to get rid of dead algae at the bottom of your pool, and brush your pool walls to remove algae that clings to the wall.

Your green pool won’t magically transform into a clear pool overnight. It’s a process.

That said, you should see a noticeable difference each day as your pool transitions from green to cloudy blue to clear. 

Perform The Overnight Chlorine Test

Once the pool is clear, you will want to perform the overnight chlorine loss test (OCLT). This test will let you know if there’s any remaining algae in the pool.

First, perform a free chlorine test in the evening when there’s no sun out, and record the levels.

Second, test your free chlorine again in the morning. If the reading has stayed the same or has dropped less than 1 ppm, and combined chlorine is less than .5 ppm, then your pool has passed the overnight chlorine loss test.

Third, if your free chlorine dropped more than 1 ppm and combined chlorine is above .5ppm, you’ll need to continue to maintain shock level and redo the OCLT the following night.

Everything’s good once you pass the OCLT test.

Now that your pool looks great again, it’s important to maintain your target chlorine level in relation to the CYA levels in the pool. 

Make sure to perform weekly pH, free chlorine, and CYA tests. 

Also, brrush and vacuum your pool weekly.

How to clean up a green above ground pool

This section details a more simplified and straightforward way to clear up the green pool for the average homeowners.

The idea here applies to both above ground pools as well as inground pools.

Step 1

First, test your water to check your pH and chlorine levels are within range. Refer to the previous section for the optimal pH and chemical values.

Step 2

Adjust chemicals and clean filters and baskets. If your skimmer and pump basket are dirty, you need to clean those. It’s also important to clean the filter so there’s a good circulation.

Next, you need to balance chemicals and pH. Depending on the pH of your pool, you’ll either want to use a pH increaser or decreaser to maintain an ideal pH level. 

Afterward, you will want to let your pump run for 3 hours. This extra time will give water time to adjust to the chemicals.

Step 3

It’s time to remove as much debris as you possibly can so they don’t use up chlorine.

Use vacuum and leaf nets during this process. This will be the part that takes the most amount of work.

Step 4

You will then shock the pool and also add algaecide if the pool is dark green. 

Algaecide isn’t going to do much If your pool just has a light green color, or if it is clear with a little bit of green splodge here and there. In fact, using algaecide under such conditions will likely be just a waste of money.

If your pool is dark green to the point you can’t see the bottom, you will definitely want to use the algaecide to speed up the process. 

Put the algaecide in the water and put however much you need depending on the size of your pool, and then let the pump run for an hour.

This will allow algaecide to mix up in the water. 

Algaecide works by swelling up the cell of algae. 

When algae swells up, it’s a lot easier for the chlorine to get rid of algae.

After you run the pump for one hour, you want to shock the pool with 3 times the normal shock treatment. 

So if you are normally shocking your pool with one pound a week, you need to shock it now with 3 pounds.

Step 5

It’s time to brush the pool down. 

That said, brushing the pool down is not as essential for above ground pools as it would be for certain types of inground pool. 

But if you see a lot of algae clumped together on the stairs and ladders, then you want to brush the bad areas where these algae are clumped together. 

After you shock the pool, you brush the pool down and let the pump run for 24 hours.

Step 6

Run the pump 24/7 until the pool clears up. The pump needs to run all day until the water is clear again.

Another common mistake is not cleaning the filters. You want to clean your filter twice a day until the pool clears.

If you don’t, your filters will clog up and you will have weak filtration. This will result in poor circulation and your green pool will take a long time to clear up.

So if you want to speed up the process, be sure to clean the filter twice a day.

Also, stay out of the pool for 24 hours since it’s highly chlorinated.

As we mentioned earlier, the clearing process will take some time.

When you wake up the next day after following these steps, your green pool should’ve turned cloudy, which is a good sign.

This is a sign that your chlorine is effectively destroying algae.

But your pool will still look cloudy because of the dead algae floating around. So it will take a few days for your pool to completely clear up.

Can you swim in a green pool?

The short answer is it is not safe. 

A green pool means there’s algae in the water, which also means there’s not enough chlorine.

Since chlorine is essential for killing off bacteria and viruses, you’ll be exposed to a sea of germs when you step into the green pool that lacks this important chemical.

You can get bacterial and parasitic infection, and expose yourself to flesh-eating bacteria. 

The green pool can be an indication of several things going wrong.

It’s possible you’re not filtering the water enough or the filter is broken.

Maybe the pH of the water is so high that chlorine can’t do its job properly. 

You may also have had some ducks living in your water, or even worse, raccoons coming by to poop in your water overnight. 

Whatever happened, you won’t know about it.

So it’s best to avoid swimming inside the green pool.

What it means if your pool water is light green

light green pool water

This is an indication that there isn’t much algae inside your pool. So you’ll just need a little bit of chlorine treatment to get your pool back into a clear state.

Dark green pool water

It signals a large growth of algae.You’ll need a proper shock treatment to turn your green pool into a clear pool.

It will also take a few days before your pool looks clear after the treatment.

What to do if your pool is still green with high chlorine

Many pool owners complain that they are putting in a lot of chlorine to clear the green pool up, but it’s still staying green. 

More often than not, they are not using enough chlorine at once.

Think of this analogy. 

If your house catches on fire, you won’t go out and put the fire out in the kitchen and go to bed, wake up the next day and start working on the living room. 

That wouldn’t make any sense because the fire would spread so quickly, the kitchen would be back on fire by the time you wake up the next day.

It’s no different with the swimming pool. 

If you don’t initially put enough chlorine in your pool to get algae out,you will kill some of it but not all. 

Over night, that algae is going to multiply and you will be back to square one. 

This is the most common reason why people struggle to clear up their green pool. It’s because they are not using a sufficient amount of chlorine at once.

For example, It is infinitely more effective to use 3 pounds in one treatment than using a 1 lb treatment once every few days.

When in doubt, go with a ‘little’ too much chlorine rather than too little chlorine.

If you use too much chlorine, then your chlorine level will just stay high for a few days, and it’s not a big deal.

If you don’t use enough, you will be back right where you started, and you will have to repeat the entire process.

how to clean a green pool with bleach

You may be wondering if there’s an alternative to shock treatment if you don’t currently have one.

In such cases, you can use bleach to fix your pool.

Around 2 gallons per 10,00 should do the job in a lot of cases.

Make sure to bleach your green pool when the sun is down. If not, the sunlight will quickly deteriorate your bleach.


Taking care of your pool is not an easy task by any means.

But with the right information and consistent, good care, it won’t be out of your reach to keep a clear pool throughout the year.

Keep calm and swim on!

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