How to Clear a Green Pool

Imagine having a beautiful pool with crystal-clear water all-year round, only to find out that the water turns green. Why is my pool green? How can I return the water condition to normal? You probably ask these questions when your pool no longer has the inviting blue color.

Algae is the most possible cause for green, cloudy pool water. Green algae are the most common one, which floats in the water or clings to the pool walls.

Black algae come as dark, slimy spots, which are harder to clean. Mustard algae look like floating sand, usually gather at the bottom of the pool.

Green algae are the easiest to remove with common chlorine treatment. Black and mustard algae are harder the remove because they are chlorine resistant. You must scrub them vigorously to “break” their outer layers. This way, the chlorine treatment will be more successful.

Protecting the pool water from algae depends on proper pool maintenance. Some pool owners are surprised to find green water even after chlorine treatment. Shock treatment (adding a large amount of chlorine) also doesn’t work if the water condition is less than ideal.

Algae are not the only organisms that ruin your pool water. Mold can grow in the pool with a poor filtration system. Other contaminants, such as debris, dust, ammonia, and other contaminants also contribute to green, murky, smelly pool water. Flourishing bacteria can also cause water discoloration.

Surprised of finding green water in your pool? Follow this guide to understand the cause and solution.

Causes of Algae and Mold in Pool Water

Swimming pool turned green because of algae and mold

Algae and mold can grow even in a chlorinated pool if the condition supports them. A brand new pool water is also green when algae and mold is already in there from the first place. Here are several possible causes of algae growth in pool water.

1. Wrong pH Balance

A normal swimming pool should have pH balance scale between 7.2 and 7.8. Lower pH scale will turn the water acidic, damaging various components. Higher pH scale will encourage bacteria to flourish, resulting in discoloration.

2. Warm Weather

Algae love warm weather, and they will flourish during warm weather. Exceptionally warm season can also encourage the growth of tougher algae, which are harder to kill.

3. High Phosphate Level

Phosphate can enter your pool through organic materials or debris. If they are left unattended, or if your filter doesn’t work properly, the materials will contribute to the phosphate level in the water.

The result is an ideal breeding ground for algae. If you don’t stabilize the phosphate level, the water will still look green even with a shock treatment.

4. Lack of Maintenance

Swimming pools with poor maintenance often have discolored water. The owners may rarely treat the water with chlorine. Poor physical maintenance, such as scrubbing and vacuuming the surfaces, can also create a good place for algae, bacteria, and mold to grow.

5. Clogged Filter System

Your pool filter system will not be intact forever. Poor maintenance and old age can lead to clogging, which prevents is from straining debris, algae, spores, and other contaminants. It results in stagnant water, which allows algae, mold, fungi, and bacteria to thrive.

When your pool water turns green, it is important to find out the possible reasons behind it. If your pool is old enough or used frequently, you probably need multiple solutions to return the clarity of the water.

Testing and Shocking the Water

Checking the quality of water can be your first step of fixing a green pool. Use several testing kits such as strip and filtration to get the detailed reading of chlorine level.

The free chlorine level (the one that is still uncontaminated) must be above 1 ppm. When it is below 1, you must conduct a shock treatment.

Make sure the water has a low pH level before you conduct the shock treatment. Consider the type of your filter before doing a shock treatment.

Use liquid treatment products for a pool with filtration or sand filter. Granular chlorine treatment products are better for a pool with DE (Diatomaceous Earth) filter. 

If you suspect the presence of phosphates, remove them first using phosphate removing products. They usually come in a liquid form.

Removing phosphates gives the pool water a “silky” feel when your skin touches it. Phosphates are also responsible for eye irritation and preventing the effectiveness of shock treatment.

Checking the Filter

Routinely check your pool water filter

When the filter is the main cause of green water, there are several ways you can fix it. 

1. Check the Filter Components

The first thing you must know is the presence of unseen damages.

Are there any cracks or faults that prevent the filter from doing its job? You should call a professional to do the job. If the filter is too damaged, you can just replace it from the beginning.

2. Clean and Unclog the Filter

The simplest way to fix the filter is by cleaning and unclogging it. Perform a backwash to remove debris buildup from behind the filter membrane. Remove any large debris and pieces, including twigs and leaves.

3. Perform a Daily Cartridge Filter Cleaning

If you use a cartridge-type filter, you need to clean it every day until the water is clean. Wash it from top to bottom using a hose, but don’t use the high-pressured one (it damages the soft filter elements).

Perform this cleaning every day until the water comes out clean. If it no longer produces clean water after several days, replace it.

4. Clean the DE Filter Professionally

DE filter is hard to clean because you must dismantle it. Unless you are a professional, you should give this task to a pool company. The company that installed your pool should be able to do the job.

After doing all things necessary to fix the filter, try running it for 24 hours. See if there are any changes in the green water. You probably need to run the filter for 24 hours every day until the pool finishes its cycles and the clean water is back.

5. Using the Algaecide

Algaecide is the most extreme solution for removing algae. You should only use it if the free chlorine level in the pool falls below 5 ppm. 

Tips to Choose an Algaecide

There are many algaecide to choose from

When you buy an algaecide, choose the one that kills the specific algae type. Green water is mostly caused by green algae, so you can buy any products that kill green algae.

Better yet, try products that kill green, red, and black algae, since they target all types of common algae with the price of one product. If your pool water is yellow or red, buy a product that has an antibacterial feature.

Check the product features in the label. If you need a quick result, choose products that say instant results. They usually remove algae within 24 to 48 hours at most (other products take weeks to remove algae from standard pools). 

How long an algaecide protects your water? Check the label to find out.

Some products can protect your water for three months, while others only last for three to four days. Also, since not all algaecide are suitable for swimming pools, find products that have “Pool and spa friendly” or anything with the word “pool” on the label.

1. Algaecide Recommendations

There are several popular algaecide products that get good reviews in 2019, which are:

HTH Pool Algaecide Super Algae Guard 60

This concentrated algaecide has a 60 percent strength, perfect for daily use. The product removes and prevents algae, keeping your pool clear and clean.

HTH Pool Algaecide reacts well with the pool water salt system. The formula is nonfoaming and you can swim immediately after applying it.

Kem-Tek KTK Pool and Spa 60% Concentrated Algaecide

Kem-Tek KTK is a great algaecide for all types of pool and filter. The nonfoaming solution is ideal for daily use. In the ideal pool condition, you can swim immediately after applying this product to the water.

McGrayel Algatec Super Algaecide

McGrayel Algatec is a fast-working algaecide solution. It immediately kills algae and prevents them from multiplying. You can clean green algae in 24 hours, but black algae need around 10 days to clean with this product.

PoolRX Algaecide Unit

PoolRX Algaecide Unit is perfect for practical regular cleaning. You can place the product in a pump basket or skimmer.

The product kills algae without adding dangerous chemicals into the water. Each application can last for about six months before the effects start to disappear.

Clorox Pool and Spa Algaecide Xtra Blue

Clorox Algaecide is one of the cheapest products for cleaning the water. It works wonder on green, yellow, and black algae. It also stops algae from growing, keeping the water crystal-clear. Clorox Pool and Spa is suitable for a maximum 25k-gallon pool.

In the Swim Super Pool Algaecide

In the Swim is a perfect algaecide to kill various types of algae, including the yellow and black ones. The product contains 23.5 percent of copper, making it a fast-acting and effective product. The nonfoaming formula allows you to swim after applying the product into the water.

SeaKlear 90-Day Algae Prevention and Remover

SeaKlear is suitable for prevention and removal, which lasts for 90 days. The formula is safe for a regular pool and spa pool. SeaKlear is effective for green, blue, yellow, red, and black algae.

Make sure to follow the instructions when adding algaecide into the water. Don’t use it if the water pH level is normal.

Cleaning the Algae Manually

Manual algae cleaning is important if their presence is very visible, especially if they form buildup or firm layers.

If your pool has a severe algae problem, you can start cleaning them manually before using other methods. Use a wire brush to scrub any spots with algae buildups. If the pool surface is made of vinyl, scrub it with a nylon brush.

After applying algaecide, you probably will see floating algae. Help your filter by removing them from the surface, using a net or pool vacuum.

Scrub the pool surfaces again to break the rest of them. Add a flocculent product if there are too many algae particles. This product binds the particles and turns them into larger masses, easier for cleaning and vacuuming.

How to Prevent Green Water

Now that your pool water turns crystal-clear again, make sure the green color never comes back. Follow these steps to keep the pool water clean.

Improve Pool Circulation

Poor circulation system will cause stagnant spots, which algae love. Create a small whirlpool by attaching a directional nozzle to the pool’s return pipe and positioning it in a specific angle. 

Adjust the Size of Salt Chlorinator

Many pool owners buy salt chlorinators that are too small for their pools. Many buy only 15 or 20-gram unit to keep the pool clean, which is ineffective (especially when the pool ages).

Make sure you invest in a salt chlorinator with proper capacity to keep your pool clean. For example, a typical 50,000-liter pool needs at least a 40-gram salt chlorinator unit.

Avoid Too Many Chlorine Tablets

Chlorine tablets contain stabilizers such as cyanuric acid. If you use this type of chlorine too often, the stabilizers will “lock” the chlorine, resulting in ineffective sanitizing action. Your water will turn green and full of algae even if the chlorine reading result shows a high amount of it.

Check and Replace Old Chlorinator Cells

Chlorinator cells can age, which reduce its function in cleaning the pool. A good chlorinator cell must produce robust hydrogen bubbles.

If the amount of bubbles looks diminished, the chlorinator cells may need replacements. 

Avoid Swimming with Dirty Body

Do you know why people must wash themselves before plunging into a pool? It is to reduce the amount of nitrogen in the water. Too much nitrogen will cause the chlorine to work extra hard in binding it, resulting in chloramines (combined chlorine). They are responsible for eye irritation, discoloration, and green water.

Keep the Pool Clean

This looks like an obvious suggestion, but many people neglect the cleanliness of their pools, until too late.

Avoid urinating in the pool, and make sure to not throwing anything into it, such as foods. Cover the pool when unused, during heavy rain, and when the sun is bright. During the winter, treat the pool with chlorine before and after the covering-up.

Regular maintenance is important to keep a swimming pool clean. Simple maintenance steps at home can also reduce the need to call an expensive professional when there are troubles.

So, Why is My Pool Green?

Green algae are the main cause of green pool water, but it is not the only one.

Yellow and black algae, mold, fungi, phosphates, debris, and bacteria can cause a discoloration in the pool. You need to conduct the right treatments to remove the green water and replace it with a clear, healthy one. 

Ask yourself: Why is my pool green? Are there any possible causes that I need to address? Understanding the possible causes helps you in finding the right products and solutions.

We will teach you how to clear a green pool in no time and with minimal effort.

We love our pools, but have you ever noticed how quickly they can turn green and, frankly, unsightly? Unfortunately, it’s become a norm among pool owners, and it doesn’t take much more than a rainstorm to do it.

Thankfully, we’ve learned how to clear a green pool fast through trial and error. After all, you shouldn’t have to cancel a pool party because of one measly storm or an overgrowth of algae.

Here are some quick, easy tips to get your pool back up to par quickly.

Regular Maintenance is Essential

It’s worth mentioning that there are a few different ways to clean your pool. It’s usually not a one size fits all solution.

Cause and severity will play a role in how the pool should be clean and how long it’ll take.

Regular, ongoing cleaning and maintenance is essential in keeping outbreaks of green water to a minimum. This includes not only the pool and water, but also your filtration system (including the pump).

Shock The Pool 

Rain tends to be the most common cause of a green pool. Usually, the water will take on a greenish tint, but remain translucent. The water doesn’t appear any thicker than usual, it’s simply a little green rather than a little blue.

In this case, a simple shock treatment should work. Just apply about 1 lb. per 10,000 gallons while allowing the pump to run overnight.

By morning, the water should return to its pristine blue self. However, it’s still not safe to swim yet; just give it about 24 full hours before jumping in.

If your pool’s algae have been allowed to fester over time (especially after you’ve uncovered it at the start of spring), a stronger solution will be necessary.

First, you’ll need either an algaecide or even regular chlorine bleach (check your owner’s manual to be sure). This will need to be distributed evenly around your pool’s circumference, just like shock treatment.

Usually, though, smaller doses of algaecide (roughly 8 ounces) will prove effective. This will kill the algae in the pool fast. 

Flock The Pool

After the algae dies, you’ll probably notice that your pool still appears cloudy. This, unfortunately, means that we’re not done yet.

After waiting about a day, it’s time to flock the pool. Essentially, a flocking solution works by binding itself to the dirt, grime and organic matter in your pool, pulling it to the bottom in the process.

This process may take an entire weekend, so plan ahead if you can. Once the flocking solution has worked its magic, the water will appear clear. However, the bottom will still look dirty and may even appear to be covered in a film.

This is the result of flocking; it pulls all unwanted particles to the bottom. Flocking is essential to get your pool water as clear as possible. 

Clean The Pool


We’d like to note that at this stage, the pool still isn’t ready for swimming yet. Jumping in now will likely kick the particles of that film back up into the water, requiring you to repeat the process all over again.

Rather, switch your pump to the “waste” setting (if it has one) and connect a pool vacuum.

It’s probably best to not use an automatic vacuum, it can take some time to clean the pool but is far more effective to go the manual route.

The waste setting will remove the pool water so you should keep a hose in the pool with fresh water coming in. ​



And that’s really all there is on how to clean a green pool fast. It’s not too terribly complicated or time consuming.

However, it’s important to follow the sequence outlined here along with any special directions listed for your pool or cleaning agents.

As an added bonus, the processes listed here tend to be affordable on any budget. And as we’ve mentioned, cleaning a pool at least once a week will help prevent significant algae from growing.

We hope this article on how to clear up your green pool fast has been helpful and will get you back in the water in no time.

You are looking forward to using your pool on the weekend after a crazy week at work, but when you get to the pool, the water looks a ghoulish green. Unless it’s St. Patrick’s Day, green water is never a welcome sight. Before you start jumping to conclusions as to how this happened, you should know that green pool water is not unusual.

What Exactly Is Green Pool Water?

Pool water turns green because of a proliferation of green algae. When you don’t use the pool for a while, leaves and other debris keep accumulating in the water. The debris, along with the heat and sunlight, provide ideal conditions for algae, bacteria and other microorganisms to thrive in the water.

Green algae in particular thrive and multiply rapidly in these conditions. These green algal blooms are what turn the pool water green. The darker the color of the water, the higher the level of algal bloom it contains.

You cannot use the pool while the water is green so the first thing you need to do is to get it cleaned out.
So how to clean a green pool? These are the 3 simple steps you need to follow:

1st Step – Scrub And Filter The Pool

Start by checking the filter and make sure it is working properly and not clogged.  Backwash it if necessary and set it to run continuously so that all the algae get filtered out.

Remove all floating leaves and debris using a hand pool cleaner.

Algae tend to cling on to the pool floor and walls. Scrubbing these surfaces thoroughly using a pool brush will dislodge the algae and break them up so the chemicals can work on them faster. Make sure you scrub all corners.

2nd Step – Treat The Pool

First, check the chlorine and pH levels of the pool water. Algal growth is promoted when chlorine levels are too low. If the test indicates that the level of chlorine is less than 1ppm, you will need to shock the water but before that you must ensure that the pH level is balanced.

If the test indicates that the pH level is lower than 7.8, you will need to add sodium carbonate to increase it. If the pH level is higher than 7.8, adding sodium bisulfate will help to decrease it. The amount of chemical required will depend on the level of pH imbalance in the water. Keeping the pump running during this process will help to disperse the chemicals throughout the pool faster.

After you’re done balancing the pH level of the water, it’s time to add pool shock, which will add chlorine to the water, killing the algae and sanitizing the pool so it is ready for you to use.

While one shock treatment may be enough if the pool water was light green, cleaning out a dark green pool may require multiple treatments.

Remember, during all of this time, your filter is running and sucking up all the small debris and algae and it is likely to get clogged after a while. Make sure you stop and clean it often so that the pressure does not build up.

3rd Step – The Final Cleanup

The scrubbing, filtering and shocking will have removed most of the algae but there may still be some dead algae stuck to the pool floor or wall. Using a robotic pool cleaner is the best way to rid of all this remaining debris and dead algae from the pool so your pool water now looks crystal clear.

Check the chemical levels one last time to ensure that all is okay before you jump into the pool.

Tips For Preventing Pool Water From Turning Green

As long as the pool is not being used and is left open to the elements, algae will continue growing and your pool water will turn green eventually. The best way to prevent this is by covering the pool when it is not in use. Other things you can do are to run the filters regularly and do periodic checks of the chlorine and pH levels to ensure that they are within the recommended range.

The worst part of being a pool owner is how quickly your pool can get filthy if you don’t maintain it. If you take care of your pool correctly, you should have no worries about your pool turning green, because it most likely won’t. However, sometimes life gets busy, and it can be easy to forget about the smaller responsibilities, like taking care of a pool, because it is not always as important as taking care of your family and your house.

For whatever reason that your pool turned green, the only thing you can do now is to take steps towards clearing it and then take preventative measures in the future. It may take a few days for the pool water to clear itself, depending on how green it is.

So, what is the reason for a pool turning green? It could be one of a few reasons, but the most common and likely scenario is that there is an overgrowth of algae in your pool.

What Is Algae and Is It Harmful?

Algae look like they are plants because of the dark green color and the way they can create a moss-like foam on the surface of your pool water, but it is an animal. They are called protists, which means they are living creatures, but are so incredibly tiny that you see them with just your eyesight. The definition of algae is a group of predominantly aquatic photosynthetic organisms.

Small amounts of algae are always in your pool, but they remain stable and unharmful as long as you maintain the balance of alkalinity and chlorine levels. It is not hard to keep the levels of pH and chlorine balanced, but it can be thrown off easily if you don’t take care of the water for several days.

The real problem occurs when the algae are overgrown and start attracting harmful bacteria and other insects to live in the pool. Some bacteria enjoy eating the algae, so they make a home in your pool, which causes the water to be unsafe for swimming.

How to Prevent Your Pool Water from Turning Green

There are three main steps you can take to prevent your pool from ever turning green in the first place. Remember that you must keep up with these steps and do them at least a few times a week, every week.

1. Clean the pool filter

On the side of your pool, there should be a pump that pulls water inside of it, runs it through a filter and back out into the pool. It keeps the chlorine circulating and clears out small debris that is floating in the water. This pump only needs to run about two hours each day, which you can set on an automatic timer. However, the pump won’t run sufficiently if the filter is dirty.

To clean the filter, close off the hoses that connect it to the pool, pull out the filter, and rinse it thoroughly with a hose. The filter is easiest to clean when it is still soaked with chlorine water; if it’s dried out, try soaking the filter in a bucket of pool water or chlorinated water before rinsing it.

2. Clear Debris Often

No matter what you do, leaves, dirt, and debris will always find its way into your pool. The water pump pulls out most of the smallest particles that float in the water, but the larger pieces, like leaves and dead bugs, will remain until you scoop them out with a net, otherwise known as a skimmer.

You can find a skimmer at your local pool supply store or online. It doesn’t matter what type of net you use since they are pretty much all the same, but if you have a bigger pool, you will want a pole for the skimmer that is extra long.

3. Test the Chlorine and pH Levels

To be able to maintain and adjust the chlorine and pH levels in your pool, you have to test the water first using a pool test kit. A basic test kit comes with a clear test block to hold pool water for comparing against the scale labeled on the side, and two dropper bottles; a red dropper bottle for pH testing and a yellow bottle for chlorine testing. Follow the instructions in the kit to conduct the tests as accurate as possible.

Once you test both the chlorine and pH, if either of the results tells you that the levels need to be adjusted, you can make changes accordingly. To raise the chlorine, you will need chlorine tablets, and to raise or lower the pH you can use either a pH Up or a pH Down solution.

No More Green Pool!

Follow those three steps of pool maintenance and your pool should stay nice and clear all year round, but if it does turn green (or if it already has), use a pool shock solution to turn the water back from green to clear. As soon as you notice that your pool is green, don’t wait to clean it. The first thing you should do is to buy a shock solution. After that, clean or replace the pool filter, and then vacuum the pool if possible.

If you have already tried everything with not much luck, the workers at a pool store can help a lot with cleaning pools. They usually allow you to bring some of your pool water into the store for them to conduct further tests, and then they can give you their professional opinion and recommendation on what steps to take to remove the green color from your pool.