What Causes a Green Swimming Pool and How to Clean It?

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A green swimming pool implies unclean green water. It might happen due to different reasons. From blue to proper green and then the water almost turning into black, these are signs of an unhygienic swimming pool. When the water is green, you know it has something to do with algae. The dead leaves gathered in the pool also play a part in turning the pool water green. To save you from skin rashes and diseases, eye infections, and whatnot, keeping a pool clean is a must. So, here we are going to discuss how to clean a green swimming pool. But for that, first, one has to know what turns the pool water green. The two points interrelate. So, what causes the growth of algae in a swimming pool, let’s find out.

Causes of Algae Growing In a Pool

A few days of not using a swimming pool causes the change in its water. You are supposed to have crystal clear water in the pool, not green. But when you do not use the pool for a few days, and the water remains stagnant, it starts deteriorating due to the growth of algae and the gathering of dead leaves. There are a few common reasons for algae growth.

Stagnant Water

Stagnant water that is exposed to the sun will turn into green within a few days. With the help of the sunlight, the raw minerals of the pool water help the algae to grow in the pool water. Then algae are known to outbreak in warm water. It doesn’t grow in cold water. Sunlight keeps the pool water warm, making it a comfy abode for the algae. 

Chlorine Level

Chlorine sanitizes the pool water as it is fatal to algae and bacteria. Dirty water means the algae will have it easy to grow in there. So, when the chlorine level is low, the water is dirty and not sanitized. Thus the growth of algae. Not only the low level of Chlorine but also a high level of Chlorine causes green pools. High Chlorine use doesn’t let the Chlorine sanitize the swimming pool the way it should. So, due to failed sanitizing, algae grows even after mixing Chlorine in the pool water. Thus, the proper proportion is vital here. The Chlorine level in pool water must be in the range of 1.0 to 4.0 PPM. To be very precise, it’s 3.0 PPM. 

pH Level

The pH level of the pool water should be 7.4 to 7.8. Anything lower than a 7, which is considered a basic, is not good for pool water. The water turns acid due to a low pH to be precise. When the pH is low, even the perfect proportion of Chlorine will fail to sanitize the water. No one wants to swim in acid. Neither an unsanitized pool full of algae and bacteria is a pleasant thing to dive into. So, maintaining the pH level is crucial. Adding soda ash or baking soda in the right proportion helps to raise the pH level. And if you have misused the chemicals and turned the pH level too high, lower it to 7.4-7.8 by adding muriatic acid or sodium bisulfate.

Avoiding Proper Water Circulation 

It is advised to always turn the pump on for filtering the pool water. The idea is to keep the water active by constant circulation. Only adding chemicals to purify and sanitize the water is not enough. The chemicals reaching every corner and edges of the pool are essential. The proper circulation that, too, for a long time will help the chemicals to spread equally in every inch of the pool. Thus filtering, cleaning, and sanitizing the water.

Cleaning a Green Swimming Pool

To keep a swimming pool clean, simply invest in an Automatic Pool Cleaner. If even after knowing why your pool water turned green, your swimming pool has become an abode for algae and bacteria, time to clean it. 

You can drain all the water, but unless it’s too green and borderline black, there is no need to drain all the water. Then cleaning is much easier than draining. Other than that, you can shock the pool to clean it.

Shock the Green Pool

Shocking the pool is the best way to get rid of the algae. So, if you are wondering how to shock the pool, then do not think far as the item that shocks the pool is not unknown to us and is bringing us back to the pool’s very favorite Chlorine. 

One needs just to sanitize the pool and kill the algae and bacteria. And which one does that the best, yes, Chlorine. Depending on the intensity of the color green, you have to decide how much Chlorine you need to mix in the pool water.

If it’s not too green, then double shocking by adding 2 pounds of Chlorine per 10K gallons of water for each shock will sanitize the water. For a medium green pool, a 3 pound per 10K gallons of water and 4 pounds for sanitizing a blackish green pool is apt.

Always shock your pool at night. Chlorine works the best when it’s dark, and there is no sunlight. Working at night also lets the pool heal overnight.

Steps at a Glance

Clean the debris, dead leaves, and branches from the pool. Scrub the algae from the pool surface, corners, and edges. 

Make sure to clean the skimmers, pump filter, and backwash the sand filter. 

Do the needful to balance the pH level of the pool water. And then add the Chlorine. 

The water will still be cloudy after the shock that is why we need flocculants at this point. A flocculants works to gather all the small particles together and creates large particles that are easily trapped in the sand filter. 

Keep the water like that overnight or for at least 8 to 12 hours. The next day backwash the sand filter. Let it constantly work for a day. And the next you will see is a pool filled with crystal clear water.

A green swimming pool is not a very pleasant sight. Diving into it is not even considered, and if someone does intend, that’s a mistake. A clean swimming pool will have fresh water in it, and the color will always be blue. Any change in color means the pool water needs clearing. And now you know why your pool water is green and how to clean it in a few steps with a few products. So, we hope you will not take the hassle of draining all the water and refill the swimming pool anymore. Instead, follow the easy way we just shared.

Clay Miller
the authorClay Miller
I am the creator/writer of and I'm an advocate for oceans, beaches, state parks. I enjoy all things outdoors (e.g. running, golf, gardening, hiking, etc.) I am a graduate of the University of Kentucky (Go Wildcats!!). I'm also a huge fan of the Pittsburgh Steelers. I was born and raised in the beautiful state of Kentucky.

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