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Getting a green above ground pool clear again (Real world advice)

Above ground swimming pools are great. Then they turn green and you can’t get it back to clear. Your pool now goes from an escape from the worries of your life and becomes THE pain of your life. I can help, but first let me qualify myself.

I have been in the swimming pool business for thirty-four years. Mostly, I have installed above grounds, but for sixteen years, I had a pool maintenance business. This is when I got most of my experience with pool water chemistry.

To get your pool from green to clear again, you must cycle your chlorine levels so that the chlorine can kill (sanitize) and then get rid of (oxidize) the green living things in the pool. The chlorine level cannot just stay high. It must go from high to zero, repeat, in order to get the pool water clear again.

My older brother had a pool service route before I did and I learned with him. I bring him up because he was kind of fearless. This means he did a lot of experimenting with water chemistry especially in the realm of getting a green pool back to clear again. Many of the extreme things he (and I) did have not been experienced by anyone that gives advice on the internet.

Most advice on the internet is in fact, more theoretical than practical. In the real world, I put many theories to the test. At the end of the day, people were paying me to get the job of bringing their pool back to clear and healthy, so that’s what I did regardless of theory. And I learned to do it well.

Is your algae yellow instead of green colored? Learn about yellow or mustard algae here


This can be a very loaded question but I’m not asking what you did or didn’t do to turn your pool green. I just mean why did it first get cloudy, then green in the natural sense.

Your pool is green because there is now a thriving existence of life in the water. A week ago when the water was clear, there wasn’t much living in the water (well there were plenty of things living in the water, but not the life we are discussing here). Now, because the water became an environment for life to multiply, it’s now so populated that you can see it with the naked eye. What you can see are green algae. You can go geek out and find the official name for it if you want, but for the sake of you just understanding how to get your pool back to clear, we’ll reference it as green algae and move forward.

There are many different kinds of algae, but green algae usually indicates that the pool went a while with a small amount of chlorine in the water, and then no chlorine. When there was no chlorine in the water, the green algae was able to have a major boost in population. I’m talking Mexico City, Mumbai, Beijing, and Shanghai all in one spot, your pool.


Again, if you want to geek out, you’ll find all kinds of information about algae. You’ll read about how many different types (and there are more than you think), how they grow, and if they are animal or plant. But Google geeking won’t get your pool back to clear and healthy. So, for the sake of actual progress, I’m going to limit algae in your pool to three kinds – green, yellow, and black.

The good news for you having a green pool is that green algae are the easiest to kill and get rid of. Usually, when a swimming pool is green, it means there was no chlorine in the water for a period of time.

Swimming pool water is a very dynamic environment for life. In reality, green algae are trying to exist and multiply in pool water all the time. When the pool has chlorine (or another sanitizer) in the water, it kills and then gets rid of green algae as it tries to exist. This is happening twenty-four hours a day, all year long.

Now, since your pool went a period of time without any chlorine in it, the green algae had an opportunity to live. And when green algae lives, it multiplies very quickly. By the time you can see a change in color in the pool, a thousand generations of green algae have populated your swimming pool.


There are two stages to bringing a pool from green to clear. The first is killing all the green algae and making sure new algae cannot exist. That’s the easy part. Then you have to get rid of the dead algae. And that’s where people have a hard time.


I’m gonna guess what happened. You went to a pool store or read some advice and then dumped a bunch of chlorine or other chemicals in the water. By the next day, the pool turned from green to a very cloudy white and you thought you were a day away from your pool being clear and healthy again. Three days went by and the pool was still cloudy. You then put in more chemicals and ran the filter longer and cleaned it often. Still, the pool stayed cloudy. After more than a week, you still had an unusable swimming pool. How close did I get?

It’s very easy to kill the green algae. You enter a bunch of chlorine into the pool and it instantly kills the green life you see and bleaches it white. It doesn’t take much chemical to kill, but it takes a lot to oxidize.


As mentioned above, killing green algae is the easy part. But how do you now get rid of all that dead life in the pool water? Here’s an explanation of the only two ways to do it.

1- Use chlorine (or another oxidizer) to oxidize to get dead algae out of the water.

What does this mean exactly? Once again, I’m going to try to make this simple for a couple of reasons. One is that I’m not Bill Nye the science guy, and the other is that having a detailed understanding of microbiology won’t help much in getting your pool back to the oasis it needs to be.

I visualize it like this. You pour a bunch of chlorine in the pool. Then each tiny bit of that chlorine grabs hold of a tiny amount of dead algae and combines with it. Then, that tiny amount of chlorine along with that tiny amount of dead algae dissipate into nothingness. At that point, the tiny bit of chlorine and the tiny bit of dead algae is gone from the water.

By this example, if you can introduce enough chlorine in the water to escort (combine with) all of the dead algae in the pool water. Then all of the chlorine and all of the dead algae will make the incredible journey into nothingness. This would leave your pool completely clear. With no dead algae (and no chlorine) in it in a manner of a day.

Of course, this is not so simple as it sounds.

2- Physically extracting the dead algae from the swimming pool

What does THIS mean exactly? This is a simple concept. Dead algae won’t leave the pool water by itself. If it doesn’t get oxidized in some way (see way #1), then it will stay in the pool water system. In most cases, pool owners will only capture the dead algae in the pool’s filter. Then, they will either backwash (sand, D.E. type filter) the dead algae out into the yard, or they will wash it out of their cartridge type filter.

Another way to physically get the algae out of the pool is to vacuum it out to waste. This means vacuuming the pool and allowing the vacuumed water to go out from the waste of the filter and into the yard.


Certainly, there is more than one way to bring a pool from green to clear. As a moderator of a large Facebook group for above ground swimming pools, I have read a lot of advice from one pool owner to another involving all kinds of specialty chemicals. Over the years, I’ve also heard of some pool stores selling various chemicals to pool owners trying to get their pools back to clear again.

Far be it of me to argue with success. If you have used some kind of additional chemical to get your green pool back to clear and healthy, then good for you.

As a pool guy, I never used anything special to get a pool to clear up. Well, I take that back. I did try some things that I had gotten for free from pool suppliers or trade shows and nothing ever helped. Once you get the concept down of killing and then extracting green algae, you realize that you don’t need to do anything except manage and cycle the chlorine levels while getting the dead stuff out of the system.

So based on this, using algaecides, clarifiers, psychics, palm readers, or any other specialty chemicals to get a green pool back to clear and healthy is a “no” for me, dog. Here’s a list of pool chemicals defined

Oh and don’t try to modify your pool’s equipment by doing something that you read on the internet like adding D.E. powder to a sand filter or something. Some filters aren’t great, but using them in the way that they were designed and manufactured will get you the best results they offer.


You don’t have to have a good working pump and filter in order to get a green pool clear, but it helps. A lot!

The reason – When water moves, it’s harder for things to live in it. This is mainly because it can get more oxygen. And things don’t live well with the presence of oxygen. Also, dead things can oxidize (dissipate) easier with movement. Stagnant, non-moving water can allow dead stuff to just sit there and ferment so to speak.

Also, a good filter can trap dead algae so you can clean it out of the pool system which helps a good deal. And, you’ll need a good pump to be able to vacuum out all the dead algae that have settled on the bottom of the pool into the yard.


By far, the biggest mistake people make when trying to bring their green pool back to clear is that they keep the chlorine level high. I know this sounds like the logical thing to do, but if you keep the chlorine level at high, it’s probably gonna take it a lot longer time before the water gets clear.

The reason you have to cycle the chlorine levels when getting a green pool clear is that chlorine can be in two states in the water. It can either be by itself (free available) or it can combine with something (combined chlorine). To help understand why you must allow the chlorine level to drop down and then go back up, I will explain what free available and combined chlorine is.

Free available chlorine

When chlorine first enters the pool, it’s all by itself. It swims around so to speak freely looking for some action. When it finds something, it can kill (sanitize) it, and then remove (oxidize) it from the water. This free and available chlorine is what you want in the pool.

Combined chlorine

When the free available chlorine finds something alive and microscopic in the water, it’s presence first kills it and then attaches itself to whatever it is. In the case of a green pool, the chlorine kills and then attaches itself to green algae.

This chlorine is no longer free. It’s now married forever to what it attached to and only unto death (dissipation) shall they part. And like a bad relationship, combined chlorine can hang out for a very long and unwanted time, smell strong, and have a toxic effect on its surroundings. Combined chlorine is NOT what you want in the pool.


No matter what condition your pool water is in, having combined chlorine in it is never good. Chlorine by itself (free available) has almost no felt presence in the pool. When it combines with something though, it starts to smell like chlorine, can irritate your eyes and skin, and bleach out swimwear.

What’s worse is that combined chlorine doesn’t do much of killing things anymore and will stay in the water instead of leaving (oxidizing). What’s even worse is that when more chlorine is introduced into the pool water, it will combine with more and more stuff. Before you know it, you have a whole lot of combined chlorine in the pool. Now your chlorine reads super high yet the pool looks terrible and is not getting better.

BREAKPOINT CHLORINATION (Read at your own mental peril)

So. I’m about to lose you here, so if you want to keep your head from spinning and just follow the steps below, then skip this because breakpoint chlorination is trippy.

Most green pools that are now cloudy and staying that way are the result of people putting chlorine in the water often and not letting the level go down. This resulted in a build-up of combined chlorine (not good). Now, when people add more chlorine in the water, guess what? Yep. Even more combined chlorine is formed. This is a vicious cycle of adding chlorine to a cloudy pool and that chlorine becoming combined with stuff. And the more combined chlorine there is in the pool, the more there will be when adding more free available chlorine. Have I repeated this enough for you to get it?

So the million-dollar question here is (if you are following me), “How do you get combined chlorine out of the pool water”?

There are only two ways to get combined chlorine out of the pool.

1 Stop adding new chlorine to the pool and let the level go to zero

This means that the pool will grow more algae and eventually overtake the combined chlorine and it will disappear. This also will usually result in the pool turning green again. Yikes! This is not good but better than what you’ve been doing.

2 Breakpoint chlorination

This is a genuine phenomenon that even Bill Nye the science guy can only theorize. For some reason, when you introduce a certain amount of chlorine in the water, all the combined and free available chlorine will just disappear.

This is great but there’s a problem. It takes a whole lot of new chlorine to achieve this. And the more combined chlorine there is in the pool, the more it takes to get to breakpoint. And it’s probably way more chlorine than the average pool owner is comfortable with pouring in.


This story may help explain. When I was in my first couple of years of having a pool service business, I didn’t know too much. My older brother started his service business about a year before me, so I learned what I could from him.

My brother Mike was fearless (He’s gone now). He was the type of person that would experiment well beyond what a normal cautious person would. Back then, he had a very dark green pool that he was contracted to bring back to clear. He tackled this in the normal way by shocking the pool with one jug (2.5 gallons) of liquid chlorine and dropped a couple of 3” tabs in the skimmer, increased the pump run time to continuous, and left.

Two days later, he returned to the pool to find it a cloudy white with a mid-level chlorine reading (3 ppm). He then cleaned the filter, poured in another jug of chlorine, and added another tab in the skimmer and left.

Mike returned in two more days to find the pool still cloudy and with a high chlorine reading. He then vacuumed the pool, cleaned the filter, added another jug of liquid chlorine, and threw another tab in the skimmer.

Four days later, he returned to a still cloudy pool and a super high chlorine reading. At this point, he now had a build-up of combined chlorine in the pool, so dropping in another jug was just going to make it worse.

At this point, Mike had two choices. He could do nothing and allow the pool to get re-overtaken with algae and thus get rid of the combined chlorine. This was not a good choice as more than a week had pasted and the pool owner was starting to wonder about the pool guy he hired to clear up his pool. He couldn’t tell his client that the pool had to be green again before he could clear it up.

The other choice was to try to achieve this thing he and I had been reading about. This thing called “breakpoint chlorination”. Knowing that there had to be a good amount of combined chlorine in the pool, he knew it would take introducing a lot of new chlorine in the pool. He decided to pour in four jugs (10 gallons) of liquid in the pool. At the time of our pool service careers, pouring 4 jugs of chlorine into a 15k gallon pool was extreme and unheard of.

The next day, Mike returned to the pool. It was crystal clear and had a very zero chlorine reading. He had achieved breakpoint chlorination and the pool was now back to clear in 24 hours. He then poured in another jug of chlorine (because the reading was zero), added another tab and the pool was now good.

That was our first victory with the concept of breakpoint chlorination and there were many more after that. Some were so extreme, that I would pour as much as 12 to 15 jugs of chlorine in a pool at once. I don’t recommend any pool owner doing this as it’s just too extreme and probably not necessary.


If you read some of this article, then you hopefully understand these three important things.

1 Combined chlorine is the enemy

2 Killing green algae is easy. Getting rid of the dead stuff is the hard part.

3 It’s very important to cycle your pool’s chlorine level from high to nearly zero to high and repeat

If you understand these three things and accept them, you are now ready to easily bring your green pool back to clear again.


This is the internet. A place where we are always complicating things. Bringing a green watered pool back to clear can be as complicated as you want to make it. I gotta tell you that it doesn’t have to be that way. If you were to pay a professional like me to bring your pool back to clear and that professional knew what he was doing, this is what he/she would essentially do.

1 Make sure the chlorine reading is zero (or close to it)

Chances are really good that the chlorine reading will be a very big zero at this beginning point. But just in case it isn’t, you’ll want to wait until it is so to make sure you’re not dealing with a lot of combined chlorine to begin with.

If the pool is green and has a high chlorine level, don’t be in a hurry. Wait until the level is zero. It won’t take long.

2 Shock the pool with chlorine, add a tablet, lower the PH

After making sure of step one, shock the pool with chlorine by either using liquid chlorine (in the yellow re-usable jugs) or granular. I recommend liquid.

You can do a bunch of math and figure out how much chlorine it takes to raise to 10ppm (parts per million) based on the number of gallons of water in your pool. Or you can just pour in a 2.5-gallon yellow jug of liquid chlorine in and if you have a normal-sized pool, you’re good. Use some muriatic acid to lower the PH of the pool if you want. Doing that will allow the chlorine to work better as a shock. Toss a 3” chlorine tablet into your floating chlorinator or skimmer. This will help prevent the pool from accidentally having a zero chlorine reading in between when you shock it next and will add some stabilizer which is ok.

3 Set the filter to run 12 hours a day

You are doing this because it’s good for the pool water to be moving while all this death and dissipation of the green algae is going on. The filter will also be catching some of the dead stuff which helps.

You are running the pump/filter only twelve hours a day because you want the pool to be off for a long enough time to allow some of the dead algae to settle on the floor of the pool. This is only so you can vacuum that graveyard to waste and into your yard.

4 Wait at least a day and make sure the chlorine reading is close to zero before shocking again

When close to zero, shock again. Add another tablet when the first one is small – You are waiting for an almost zero reading to make sure the pool doesn’t get a build-up of combined chlorine. If you don’t know what I’m saying here, please do yourself a favor and re-read what I cover above.

5 When the pump and filter have been off for a while, vacuum the pool to waste

Let’s say you are running the pump for 12 hours starting at 9 am and turning off at 9 pm. Wake up early and vacuum the pool to waste an hour or so before the pump turns on at 9 am.

You do this because the pump has now been off all night and the stillness has allowed some of the dead algae that were suspended in the water to fall down to the floor of the pool. You can now vacuum that stuff directly our of the pool system. This makes for less dead algae for the new chlorine that you are putting in the pool to have to oxidize.

This is very crucial so don’t skip this step because its a pain to vacuum to waste. Remember, removing the dead algae is the hard part. Vacuuming it to waste and into the yard is extremely helpful to get the pool clear again.

6 Clean filter

Cleaning your pool filter gives you an opportunity to get more of the dead algae out of the pool and system. Do this as often as you want but once a day should be enough. NOTE: Some filter types are better than others for helping to bring a pool back to clear. Learn the different filter types here.

7 Repeat steps 1-6 until the pool is clear

As the pool begins to clear up, there will be more and more time in between steps. Keep in mind that you are getting the dead algae out of the water. This is being accomplished by the chlorine oxidizing it, you vacuuming it out to waste and into the yard, and cleaning the filter out and into the yard. Be patient and don’t try to hurry it up. It could take 2 days or two weeks depending on how much green algae you had to begin with and how good you are with these steps.

8 When the pool is clear and clean, return the pump run time to normal, decide why you think the pool turned green to begin with, and make some changes

Congratulations! You made it. Now learn from your past and figure out what you did (or more likely what you didn’t do) to allow the pool to turn green.

You don’t want to go through this again, so make some changes. And if you go on vacation, do these things to prevent the pool from turning green when you get back.


Dan writes with the knowledge of having 35 years (and counting) in the above ground pool industry.

17 thoughts on “Getting a green above ground pool clear again (Real world advice)

  1. Point break chlorination is also used in wastewater treatment for ammonia levels, extremely expensive and I have used it. Terms used are free and residual chlorine in water treatment. If maintained, no issues, if not you will have serious issues. Does anyone check for ammo is, NH3 in pools? Crazy if you don’t.

    1. I installed a pool for a guy who ran a wastewater treatment facility in upstate NY for like 30 years. He told me a lot of things that I don’t remember about the differences between his job and managing pool water. It was interesting. And no one that I know of checks for ammonia levels in pools. The closest I’ve gotten is checking for nitrogen levels(from fertilizers) due to not being able to keep a chlorine reading.

      1. I have been battling algae all season. Sand filter (new sand and new pump this year). Green and cloudy. Yesterday, my chlorine was at zero and I added one gallon, thinking I am doing the right thing. Floater is full. Today, Chlorine is through the roof. If I am understanding this very informative article, once Chlorine gets to very low or zero, I shock it again?

        1. Yes wait until the chlorine level is low. I don’t want your floater to be full of tablets though. You want to give the chlorine a chance to go down especially when fighting a green or cloudy pool. If a smaller pool (smaller than 24′) then maintain only one tablet. If bigger than 24′, then 2 only. And don’t forget to vacuum to waste. It’s very important to get that dead stuff out of the pool so the chlorine doesn’t have to work as much oxidizing it.

          1. I have an 18×48 and am wondering if I can vacuum it from inside the pool while cycling the chlorine? Its really hard to vacuum unless I am in the pool. I have both a water vacuum and a vacuum that connects to my filter.

            Am trying to get my pool cleared as well.
            Thanks for all your help.

          2. You can vacuum from inside the pool, but it’s not ideal. And keep in mind that it’s crucial to vacuum that dead algae completely out of the pool and into the yard. In any way that you have to.

  2. Thank you for you advice and saving us so much money. We have a Perma Salt filteration that was suppose to be less maintenance but 3 months later and still at square 1. Can you give me advice?

    1. I plan on writing a few articles on chemical maintenance this fall. Please check back for that. In the meantime, reading the “green pool” article will teach you how to cycle your chlorine level, which is the trick to everything.

  3. 18×48 above ground summer waves pool, bought an intex Krystal clear 10 in sand filter… was great until it died, now I have another and swamp water, and the pool guy stopped doing AG pools yeah!! chlorine is zero, ph is sky high 8.5+, added ph down 1.25 cups by Clorox at 8pm/ tested at 10 still sky high, added second dose retested at 1am – no change, decided to go to bed, 7am retested went down slightly like guesstimate based on color chart 8.2 maybe?? I added third dose. Directions say not more than 40oz in a 24 hr period for 10k gallons, I have my gallons at 7,630.2 roughly, so 9.18 oz three times is roughly 27.5 oz…I’ll retest at 10am..I’m hopeful something happens. I know my ph needs to be neutral 7.2-7.4 in order to shock/chlorinate my pool appropriately. The filter is currently on 12 hr cycle… I’m backwashing every 4-6 hrs, the gauge is barely creeping to yellow but the water that comes out is green green. Sorry for the book, the FB is awesome and I’m in it now but I really need legit info please help! Oh the test kit is the 3-1 Clorox kit and I’m using their app.

    1. Cycling the chlorine is more important than what your PH is at. If your PH isn’t lowering, then use liquid muriatic acid.

      If chlorine is at zero, then good. Pour in a yellow jug of liquid chlorine(2.5 gallons) and one 3″ tablet. Don’t add more chlorine until almost zero again.

      Run pump 12 hours a day. Vacuum the bottom of the pool to waste after about 10 hours of the pump being off. If not much dead algae on the bottom, wait until the next day or two to vacuum out the dead stuff when there’s enough.

      You have a really undersized filter and pump with those pools which makes this process very hard. Being able to vacuum out the dead and fallen algae well is key, so if you’re not able to do that well, then this will take much longer to go to clear. Remember that most of the chlorine is used to oxidize(get rid of), so vacuuming dead algae out into the yard is very important.

  4. Has anyone ever had a chlorine lock? If so what do you recommend? We had our water tested and the Cyanuric Acid level was at 290ppm which it is suppose to be between 30-100ppm. We purchased BioActive which is a CYA reducer instead of draining half of our pool. Has anyone ever had this happen??

    1. I’m not familiar with that product. I have rarely encountered too high of cyanuric acid levels because I never add it independent of what is in the chlorine tablets.

      There’s no harm in trying that product, but if it doesn’t work, then drain the pool down and in the future, don’t add any CYA and limit your tablets. It is crucial for chlorine levels to cycle down to almost zero often, so trying to keep a proper level of CYA can be dangerous and completely unnecessary.

      1. 24 round aboveground pool 4 ft to 6 ft. Looks like your picture mabye mabye murkier 2 days ago put 12 gallons of bleach from pool store. The water looks no better. It also testing water looks like no chlorine. Im confuses should this still be the green color if its dead algae

  5. I’m having trouble with my pool 18×48. My store sold me 57 dollars worth of chemicals. No better at all. My son in law used his portable pump to help circulate, he also flushed some water in while circulating and removed dirty water with hose. Needless to say i decided to just empty the pool and starting over in the next few days. What should I put in pool when filled. When I opened pool I spent 150 dollars on chemicals.

  6. I have an Intex round Ultra XTR® Frame Above Ground Pool w/ Sand Filter Pump – 20′ x 48. This summer has been the worst for green algae. In reading your article, I felt like you were standing in my backyard for the last month watching me work on this pool. Shock, vacuum to waste, refill the water, next day its cloudy, added more chlorine, still cloudy, then 2 days later it’s getting green again, and next day it’s pea soup. It has truly been a struggle. My pool is now pea soup, so I am off to Home Depot to get 10 boxes of chlorine, 3″ tablets, and I am going to follow your instructions step by step…..I will keep you posted. Thank you for making it so simple.

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