Green to Clean: How to Clear Up a Green and Cloudy Swimming Pool

Updated on March 5, 2018
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Rob is a licensed pool service industry professional with over 20 years of experience.

An example of green pool water that can be cleaned chemically.
An example of green pool water that can be cleaned chemically.

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Help! The Pool is Green!

Treating a pool that has turned green? This article will get you step-by-step through how to get that nasty pool in shape. I will also cover some basic chemistry and filtering tips to prevent this from happening again.

All information is based on an in-ground home pool of average size, from 12 to 15 thousand gallons.

Six Steps to a Clean a Green Pool

  1. Determine whether your water chemistry is fixable or whether it's too far gone.
  2. Test the water to determine the PH balance.
  3. Shock the pool.
  4. Pump and filter to regain balance.
  5. Brush and filter.
  6. Maintain balance.

Each of these steps is described in detail below.

How "Green" Is Your Pool?

Because if it's too green, you may need to have it drained and acid washed. I have seen many pools that were not just green, but black. In severe cases like this, it is more cost-effective and less time-consuming to simply drain the pool and have it acid-washed. People sometimes do not like this approach because of concerns about the cost of refilling the pool. The choice also depends on the type of filtration you are using, which I will cover.

This is my general rule for determining whether the pool can be treated chemically or needs to be drained: if you can see at least six to eight inches below the surface of the water, most likely the pool can be treated chemically. An example is in the picture at the right above; you can see the top of the first stair down into the pool, depending on the water level. Once we establish that the pool doesn't need to be drained and can be treated chemically, we can go from there.

Step 1: Testing the Water

If the pool is green, obviously there is very little to no chlorine in the pool. So testing for chlorine is not very important, since you'll be shocking the pool anyway. But pH plays a very important role. If the pH is very high, the shock will turn the pool cloudy. (It will be cloudy anyway until it all filters out, but high pH will cause a VERY cloudy pool when using shock.) I prefer to use a higher-end test kit, but the cheap test strips will at least give you an idea if your pH is high or low. You want it to be low. If the pH reads high, use one gallon of muriatic acid, which should be enough. Don't worry about adding too much acid. Test the pH again after shocking and 4 hours of circulation.

Step 2: Shocking the Pool

Once your pH is 7.2 or below, you are going to start by shocking the pool with granular chlorine (calcium hypo-chloride). I suggest purchasing a 25-pound container of granular chlorine, rather than the individual one-pound bags they sell at pool stores or large chain stores. You'll save a great deal of money, and you will need the chlorine in the future for small doses from time to time. Use five pounds of granular shock, or 10 gallons (four 2.5-gallon jugs) of liquid chlorine. With the filter pump on, broadcast the chlorine evenly over the water covering the entire pool surface until all five pounds of shock or all ten gallons of liquid chlorine have been used. Be sure to use a good algaecide as well, which you can add after a few hours of circulation.

Step 3: Pumping and Filtering

What type of filter do you have? Follow these steps for your type of filter:

  • Diatomaceous Earth (DE) Filter: Before anything, backwash the DE filter. Add fresh DE powder, shock pool as explained above and run the pump for 24 hours. Make sure there are no obstructions on the pool drain, such as leaves. Of course, because the pool is green, you can't see the drain, so just run a brush over the approximate place where the main drain is at the deep end of the pool.
  • Sand Filter: Same as DE, except the backwash time should be a minimum of five minutes.
  • Cartridge Filter: Make sure it's in good condition and rinsed thoroughly. See note in Step 4 below about cartridges.

Step 4: Brushing and Filtration

After 24 hours of chemicals and circulation, you will see an amazing transformation. Your pool should not be "green" anymore. But it will still be cloudy, and it will need a lot of brushing and filtration for the next few days. There will probably still be a few stubborn isolated green areas that need some brushing. After 24 hours of constant circulation, backwash the filter.

Special note for cartridge filters: they will need to be cleaned more often than other filters during this process: twice a day for at least two days, or until the pool is clear.

Step 5: Maintaining Your Pool

Tips for maintaining your pool:

  1. Use a water clarification solution.
  2. Make sure you have a reliable chlorinating system, whether it is an in-line, floater, or salt system. Chlorine needs to be in the pool always. Throwing a jug of liquid in it once a week isn't a good way of maintaining the pool. A simple tablet chlorine floater is very effective. You can purchase one on eBay for a reasonable price (see below).
  3. Clean your filter. DE filters are by far the best filter to have. Although a bit more costly to purchase at first, they will save you both time and lots of money in the long run.

Normal Filter Maintenance

  • DE filters: Backwash once a month
  • Sand filters: Backwash once every two weeks. (Be sure to backwash your sand filter for a minimum of four minutes. Otherwise, you will see filthy water shooting back into the pool.)
  • Cartridge filters: Every three to four weeks, unless you see algae in the pool, in which case you should clean more often. Soak in tri-sodium phosphate every three months.


You may want to check out my new article, which covers frequently asked questions such as:

  • Why is my pool still cloudy and green when the chemicals are right?
  • I shocked the pool, but it's still green.
  • How much shock should I use?
  • How long should I run the pump after shocking?

And my other article answers this common question:

  • How much acid should I put in the pool?

Questions & Answers


Submit a Comment

  • robhampton profile image

    Rob Hampton 3 years ago from Tampa Bay, Florida

    Johng743 thank you for your comment, but not quite sure what you mean.

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    Johng743 3 years ago

    You are my inspiration , I have few web logs and very sporadically run out from to brand. geeceddagkdf

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    BarneyBM 4 years ago

    I totally agree with robhampton, empty your pool, clean it and fill it with fresh water. I read an article of a person cleaning his son's pool, took him almost a month and liters (a lot!) of bleach, anti algae and who knows what (oh and not to mention the bottles of wine he consumed waiting for the pool to turn from green to blue). I will never swim in that pool, it will kill me!

  • robhampton profile image

    Rob Hampton 4 years ago from Tampa Bay, Florida

    @Traceylee...If you use well water, first you need to be sure the pool water is free of metals. Well water has a high concentration of certain metals. .. Iron, Copper, Magnesium, Chromium, lead, etc.. It can be devastating if you shock a pool with high amounts of metals. There are products you can purchase to rid the pool of metallic content. I've actually turned a pool black (the actual finish turned black) in my younger days by shocking it without testing the metal content. Luckily I was able to fix it with citric acid. Just get a quart or two of metal remover before shocking, circulate for 24 hrs, you'll be fine

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    Traceylee 4 years ago

    What if you used well water in your pool and shocking or adding chlorine makes it turn green...or brown depending how much shock was used..

  • robhampton profile image

    Rob Hampton 4 years ago from Tampa Bay, Florida

    @Michele..Thanks for inquiring. Sounds like a drain/clean and acid wash to me. If you have anything other than a DE filter, then you will need to drain the pool. The cost of re-filling a pool is not as costly as most people would assume, so don't let that scare you. Less than $100.00 for sure (unless you have some crazy Olympic sized pool) If you have a DE filter, it can be cleaned chemically. let me know if you have any questions at all. I can walk you through both the drain/clean process as well as a chemical clean. Just shoot me an email. Good luck...Rob. . .

  • profile image

    Michele 4 years ago

    We had some eletrical issues and our pool pump was down for 2 weeks. We live in Florida and between the heat and rain our pool is now black. I put 2 shock treaments in it, but that did nothing. Was going to go get chlorine to put in pool. Should we drain or can we treat to get blue again? Thanks for your help!

  • profile image

    Clayhounds 4 years ago

    Nicely written Hub. Also like all the links. By the way, I do have a swamp pool that I will try these steps

  • robhampton profile image

    Rob Hampton 4 years ago from Tampa Bay, Florida

    Dr alex murray.... That is one of the weirdest comments I have ever seen. Sounds like you are counterfeit money maker? Hopefully the feds will give you a call.

  • robhampton profile image

    Rob Hampton 5 years ago from Tampa Bay, Florida

    Cheryl, I hope it helped, thanks for the comment. I'll be sure to check out your site. Rob

  • swimfan profile image

    swimfan 5 years ago from United States

    Awesome step-by-step guide. Seems like this is an issue that plagues a lot of pool owners.

  • robhampton profile image

    Rob Hampton 5 years ago from Tampa Bay, Florida

    I suggest highly that you drain and refill. It would cost far less than spending money at those pool stores that try to sell you stuff you don't need. The other alternative is a flocking agent, or "drop out" or "drop and vac" This will sink all of the algae to the bottom of the pool and will need to be vacuumed out to waste. Does your sand filter have a multi-port valve in order to vac to waste? I would consider installing a cartridge filter as well. Will save you a lot of headaches.

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    Pixtaker 5 years ago

    what do I do about an above ground pool that has the same problem? We've sunk at least $300 at the pool was clear for 2 weeks, then slowly returned to this pea soup state even while maintaining....we have a sand filter and i can see the top stair almost the second....

  • robhampton profile image

    Rob Hampton 5 years ago from Tampa Bay, Florida

    Johnr54, Thank you for your comment. Battle is a good word for that. I know how difficult cleaning up a pool can be sometimes. Glad to hear you finally have it taken care of. Feel free to post any questions you might have in the future.

  • johnr54 profile image

    Joanie Ruppel 5 years ago from Texas

    Very useful hub. I am a widow taking care of a big pool that we use often. I use a pool company to maintain the pool, but am happy to read more about what to do for a green pool. I am happy to say we are crystal clear after 6 weeks of battling the green!

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    Richard Stephen 7 years ago

    I've had to go through this process a couple of years ago. Your instructions are basically what I did too. The improvement after 24 hours was amazing and the pool looked great after 3 to 4 days. It is important to clean the cartridge filters (if you have them) as the algae will clog them and make your pump work too hard. After a few days of filtering, a clarifier will help clear up the cloudiness. Good hub!

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    Karen Reader 7 years ago

    From green to clean, I like that! These are some great tips on taking care of your pool. Thanks for sharing.

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    Pool Chemicals 7 years ago

    Great hub. Breaking this down into steps definitely makes it easier to understand. Thanks for sharing.