How To Clear Green Pool Water (And What Really Caused It)



Swimming pools can be tailored to a specific aesthetic , from the shape and size of the pool, to the landscaping around it, right down to the color of the water.

But when we talk about fixing green pool water, we’re referring to dirty pools where the water suddenly changed, making it toxic to swim in.

The first thing you need to figure out is…

Why Is Your Pool Water Green?

Hazy and uninviting, you’ll know something is seriously wrong with your pool water when it starts to turn a nasty shade of green.

Why is this happening? 

There are several reasons why pool water can look this way, but the following are the main culprits:

It’s Probably Algae

Algae in pools can be a big problem. Many owners use algaecides as a preventative measure to keep algae from even getting into their pool.

Once it’s in it can be hard to eliminate, and it can lead to extra maintenance and even staining of your pool’s finish. Due to its microscopic nature, it’s only when algae has gotten so out of control that you even begin to notice it.

There’s three types of algae that can accumulate in your pool water: green algae (green color), mustard algae (yellow-green), and black algae (dark green).

Although they’re all worth your attention, green and mustard algae are the ones that cause a dramatic water color change.

Soaring temperatures in the summer months, coupled with a lack of chlorine in the pool will encourage algae to bloom. It can be free-floating in the water, hangout on the surface, or cling to the walls and floor.

Ironically, algaecides that contain copper sulfate can be the reason water has turned green – which brings us to our next potential culprit…

But It Could Be Copper

Issues with metals being present in the water, specifically copper, can be the reason your beautiful pool looks unwell.

This is actually a common occurrence with new pools after filling them up and shocking the water. What’s happening here is the chlorine from the shock is oxidizing the copper in the water. 

It’s similar to historic buildings with green roofs, or The Statue of Liberty – they’re actually made of copper. Their prolonged exposure to oxygen resulted in oxidation of the metal, which gives them the green look we’re familiar with.

Well water in particular is susceptible to this problem, as it contains high metal levels. A relatively cheap solution is to use a bobby hose filter when filling up the pool, which is a mono-filament propylene material and the same kind found in a pool’s DE filter.

By attaching it to your garden hose, it helps filter metals as the water passes through it.

Or Even Pollen

To a lesser extent than the first two culprits, but not to be discounted, is good ole pollen.

Pollen is green or yellow in color. Yellow mixed with blue water, will create a green tint. Pollen doesn’t float on the surface or cling to walls, but it will float in the water until you get rid of it.

Causes of pollen in your pool? 

If your filtration system is stagnant for too long, this can lead to pollen building up in your water. That’s because your backyard is full of pollen-heavy foliage and vegetation. If the filtration system is off for long periods of time, the water won’t circulate and impurities like pollen won’t be filtered out.

Additionally, skimming of the pool may need to be increased. This can be done by investing in an automatic pool cleaner or vacuum to help keep the water clean. 

Finally, if your pool filter system has been regularly running but the pollen isn’t being removed, check to make sure the filters aren’t clogged and dirty. If they are, they’ll need to be cleaned/replaced.

How To Fix Green Water Caused By Algae

Got an algae problem? It might take some time, but here’s how to fix it.

Step 1. Test & Balance Your Pool Water

First thing you need to do is test and balance the water in your pool. Using test strips or a liquid test kit, make sure the pH level of the water is at 7.8, by raising or lowering it accordingly. Also, your chlorine level needs to be adjusted so that it’s sitting over 1ppm. 

Step 2. Clean Filters & Run The Pump

It’s recommended to clean your pool filter as it might be clogged from months of use. This process is different depending on your type of filter, so make sure you clean and rinse your cartridges, and backwash a sand filter or DE filter.

You’ll also need to run the pool pump non-stop during this process so that algae doesn’t re-form. When pool water isn’t circulated well, or often enough, algae blooms.

Step 3. Remove Debris

Time to introduce a little elbow grease. You’ll need a net skimmer, a pool vacuum, and a pool brush. Use all three to get the pool clean, and remove as much dead algae and debris as you possibly can.

Make sure your pool brush can be used on your pool walls, as you don’t want to damage a vinyl liner with steel bristles, and you don’t want soft bristles to be ineffective on a concrete or plaster finish.

Step 4. Shock The Pool

Next up is to destroy every living organism in the water with a massive dose of pool shock treatment.

You’ll need to either mix granular shock with water, like calcium hypochlorite shock, or use liquid chlorine – both of which get poured into the pool. In any case, it’s important to wear gloves and follow safety protocols when handling any pool chemicals.

The pool should test under 3 ppm before you even think about getting back into it. Also, only shock at night, as the sun’s rays will burn shock chlorine quickly as it doesn’t contain cyanuric acid.

Step 5. Retest (& Possibly Repeat)

At this point, retest the water and repeat the entire process if the pool isn’t crystal clear. You may also try adding pool flocculant to clump up algae and other particles, as well as using algaecide for controlling future algae blooms.

How To Fix Green Water Caused By Copper

Resolving green water caused by copper is a more analytical approach that requires some chemistry to change the chemical levels in the water.

Step 1. Test Copper, pH, and Calcium Levels

Using a test strip that’s specific to copper, dip it into the pool to find out the amount of copper in it. Ideally, you want it to be at zero. Next, test the pool’s pH level with a regular test strip or liquid test kit.

A pool’s balanced pH should be between 7.2 and 7.6. Finally, use a calcium test strip to find out the level of calcium hardness in the water. In general, you’ll want this level to be 250 ppm.

Step 2. Run The Pump & Adjust Calcium Level

Turn on the pump and let it run for at least 8 hours. Calcium is your friend in the fight against copper, so use calcium chloride to raise the level to 350 ppm if it’s low. 

With calcium chloride, 2 ounces per 1,000 gallons will raise the ppm by 10. So if you want to raise it 50 ppm, use 10 ounces per 1,000 gallons.

Step 3. Balance The pH Level

A pool needs to have a balanced pH level in order for the water to be sparkling clean. If the pH is too high, you’ll need to lower it using muriatic acid.

If it’s too low, you’ll need to raise it with sodium carbonate. There are products on the market like pH Increaser or pH Decreaser that can help you do these relatively painlessly. 

Finally, re-test the water until all the desired levels are reached and at this point the pool should no longer be green.

How To Fix Green Water Caused By Pollen

Getting rid of pollen is the easiest of the three, and pretty much only requires basic maintenance.

Step 1. Filter & Skim

Begin by running the pump so the filtration system can catch the pollen as it leaves the pool.

While it may not get rid of it all, it can catch quite a bit. You’ll also need to start skimming the surface of the pool every morning with a fine mesh skimmer to catch the smallest particles possible. During pollen season, skim multiple times per day.

Step 2. Add Chemicals

Some pollen will be too small to catch with a filter or mesh netting, so adding in aluminum sulfate will be helpful.

This chemical binds to pollen particles causing them to clump together, making the job of the filter or skimmer a lot easier.

Step 3. Vacuum (If Necessary)

Vacuuming your pool can be time consuming and costly, but if you still have water pollen this should get rid of any that’s remaining.

Keep in mind your utility bills will go up as you need electricity to run the vacuum, and you’ll have to replace the pool’s depleted water. As usual, test and balance the water after you’ve re-filled the pool.

Let’s Talk Prevention

With various culprits causing green pool water, it can be tough to nail down the cause, and even more challenging to treat it. This is why taking a preventative approach is so important to keeping your pool water healthy.

Pool Cleaning

As a pool owner, you need to be a responsible one, and part of that responsibility entails adhering to a schedule for pool maintenance.

Cleaning your pool on a regular basis is going to be the best preventative measure you can take to ensure there are zero issues with your pool water. If problems do arise, you’ll quickly be on top of them. 

Cleaning a pool can be fairly painless just by installing an automatic vacuum to do a lot of the work. But you should also scrub the walls with a pool brush, and use a net skimmer on the surface to keep the level of debris buildup down.

Water Chemistry

When it comes to the chemistry of your water, you don’t need a degree from a prestigious University to properly balance chemical levels.

But you do have to be aware of the water’s pH level, the water’s alkalinity, and the levels of the sanitizers you are using (ie. chlorine, bromine, etc.)

This can be done through water testing at least once a week using either test strips or liquid test kits. They’re both fairly inexpensive and give you accurate levels so you know where your pool is sitting at, and what chemicals may need topping up to get the pool chemistry back to a balanced state.

Water Circulation

Pool water cannot remain stagnant. If it does, you’re going to see issues develop, as things like algae love a stagnant environment. Water circulation is critical as it not only mixes up the chemicals in the pool, but it distributes them evenly. This ensures things remain balanced and there are no dead spots that aren’t being sanitized.

Part of water circulation is also filtration, as the pool water must be pumped out of the pool, put through a filter (which removes particles and debris), and is then injected back into the pool via its return jets. So, you want to make sure your pump, filters, and return jets are all performing at 100%.

Circulation can also be improved if you have water features like bubblers, deck jets, or pool coolers. These will all increase water flow so the pool isn’t sitting still for long periods of time.

Green Today, Gone Tomorrow

Green pool water is unsightly and disheartening, but it’s not a death sentence for your pool.

By properly identifying what turned your pool green, you can take the appropriate steps needed to clear up the water, restoring it to it’s majestic aesthetic and making it safe for swimming once again.

Categories: Pool Care, Pool Problems