11 Reasons Why Your Pool Keeps Turning Green

Reasons Why Your Pool Keeps Turning Green

A pool is an important part of your home. Swimming is healthy and exciting for recreation. It is the best place to have a cold drink after a hard day’s work. It’s disheartening to head to your pool to get a refreshing dip, only to find your pool water has turned green.

Swimming in green water isn’t healthy and can cause skin irritation or eye infection.

To get started fixing the water, you need to know what’s wrong. To help you determine what’s going on with your pool, here are the 11 main reasons your water turns green.

What Causes Green Pool Water?

1. Frequent Rain

Rain isn’t bad for your pool because it lowers the concentration of chemicals such as calcium and cyanuric acid in the pool. However, excessive rainfall may cause a chemical imbalance in the pool. The rain itself is acidic, with a pH of about 5. When rainwater gets into your pool, it may increase its acidity and lower the chlorine level in it.

But that’s not all. Rainwater also comes with dirt and organic particles that can alter your pool’s chemistry. This means that rainwater can cause the growth of algae and other microorganisms in the pool, causing the water to turn green. Cleaning your pool regularly is the best way to prevent the negative effects of rainwater.

2. A Low Level of Chlorine in Pool Water

The absence of chlorine or low chlorine levels is one of the most common reasons pool water turns green. The actual cause of the green color is algae, which blooms in the absence of chlorine. Algae can grow exceptionally quickly and turn your water green in less than 24 hours. This happens mostly in warm weather.

On average, the chlorine level in the swimming hole should be between 1 and 4 ppm. Keep testing the chlorine level in your pool to confirm whether it falls in this range. If not, you can use one of these to increase the chlorine levels in the water:

  • Powder shock
  • Liquid shock
  • Granular chlorine
  • Chlorine tablets

This will eliminate algae from the pool and prevent it from turning green.

3. Over-Stabilized Water or Very High Levels of Cyanuric Acid (CYA)

Cyanuric acid is used in pool water stabilization. It’s a chemical that reduces the rate at which chlorine degrades in sunlight. It acts like sunscreen for the swimming pool. However, if you use excess cyanuric acid, it will interfere with chlorine, preventing it from sanitizing the pool water. This means that over-stabilizing your water will provide a conducive environment for algae to thrive, turning your lovely swimming spot green.

The recommended cyanuric acid concentration is between 30 and 50 ppm. If your concentration is higher or lower than this, you have to bring it back to the recommended levels. For higher than necessary levels, you have to drain off some water and replace it with untreated water.

After checking Cyanuric acid levels, you should use chlorine to sanitize the pool rather than using chlorine tablets or chlorine floaters, two chemicals that contain Cyanuric acid. Alternatively, you can use salt water with a chlorinator in your pool to prevent cyanuric acid from getting into your swimming hole.

4. High Phosphate Level

Phosphates are among the chemicals that make algae thrive. Phosphates can get in through garden runoff, organic debris, and fertilizer. Apart from encouraging the growth of algae, phosphates also reduce chlorine levels in the water. This means if you don’t treat your pool, the levels of chlorine will go down faster than anticipated in the presence of phosphates.

Continue testing your water to determine phosphate levels. If it goes beyond 500 parts per billion, use a phosphate remover to lower its levels. You can then use the right chemical to boost chlorine levels to ensure the water is well sanitized.

5. Pollen Grains

If you have flowering plants nearby, the pollen grains they produce can be carried by wind and deposited in the pool. This can make the water look green. Pollen grains are tiny, making it difficult for them to be retained by the standard filters. This means if you don’t clean your pool regularly, pollen will build up in it.

Pollen floats on water, and you can mistake it for algae. If you don’t remove it, pollen will increase the level of phosphates in the water and lower the chlorine level in it. The net effect is that the water will turn green.

Though pollen is harmless and you can swim in it, those particles will make your outdoor space look unsightly. There are many methods of removing pollen from water. Some methods include:

  • Skimming the water regularly
  • Adding aluminum sulfate
  • Shocking the pool, and
  • Vacuuming the pool.

6. High pH Level

Chlorine makes your water acidic, so it will be rendered inactive when the pH is high. That’s why you should not allow your pool pH to reach 8.2 or more. The pool’s pH is likely to increase when using a chlorinator, which is very common in saltwater maintenance.

To prevent this problem, test the pH regularly and correct it if it’s too low or too high. The recommended pH range is between 7.2 and 7.8. If the pH is too high, use pool acid to bring it down.

7. Poor Filtration

If your pool filter is damaged or you don’t run it for the recommended duration, dust and other organic debris will build up in the water, creating an environment that encourages algae growth. This will make the water turn green. The filter should run for no less than eight hours a day in warm weather.

You can always invite an expert to check the filter to ensure it’s in good shape. If you are using a sand filter, do some back-wash once in a while to clean it. The filter can get clogged with organic matter, which may end up in the pool.

8. Dissolved Metals

Dissolved metals are another reason for green. The main culprit here is copper metal. When this metal gets into your swimming water, it will turn the water green when it gets oxidized. Copper can get into the pool through your water source. For example, well water is mineral-rich and contains a high percentage of copper.

Another way copper can get into your pool is through accessories such as the heating system or metal ladder fitted into the swimming hole. Copper gets oxidized when the water is highly acidic. This mainly happens after a shock treatment.

If you don’t treat your pool, the levels of dissolved metals in it can worsen, causing stains on the finish and fitting of the swimming hole. You can use specialized products to remove dissolved metal from water to prevent it from turning green.

9. Larger Debris and Contaminants

Grass clippings, tree leaves, and birds’ droppings are organic matter that supports algae growth. As you cut the grass around the pool, some grass cuttings may get into your water. Nearby trees are also likely to lose leaves that the wind can carry into the pool. Another issue is birds’ droppings that fall directly into the pool.

Debris, dirt, and other contaminants will inevitably fall into your pool. Winds can transport soil from great distances. Dirt and debris provide an excellent environment for algae growth that can turn your pool green.

All these can be prevented by covering the pool when possible. Alternatively, when leaves do enter the pool, it’s important to remove them quickly either my raking them out or vacuuming.

10. Using Copper-Based Algaecides

As already mentioned, copper is one of the metals that can make water turn green. In an attempt to remove algae, you may use excess copper-based algaecides, which may increase the copper levels in the water. If that happens, the water will turn green.

The solution to this problem is to use metal-free algaecides. If you have to use copper-based algaecides, you have to determine the right amount to use so that you don’t have any excess copper in the water.

11. Failing to Use Clarifiers or Flocculants

After shocking your pool, the water should be clear, and you should be able to see its bottom. If not, adding a flocculant or clarifier may be necessary to help remove dead algae that makes the water dirty.

A flocculant is a chemical that binds to tiny particles in water, clamping them together so they can become heavy and sink to the bottom. A clarifier is a product used to remove the cloudiness in the water, making it shiny and clear.

Both clarifiers and flocculants bind microparticles, thereby creating larger particles that can sink. Once these larger particles formed by clarifiers sink, you can remove them through filtration. In the case of flocculants, you may need to vacuum to remove the particles.

Get Rid of the Green This Summer

Algae is the leading cause of the green color in pools. It’s not healthy to have these microorganisms in your swimming water because they encourage the growth of bacteria wherever they are present.

When you notice your pool water turning green, act fast to correct the situation. Consider these reasons your pool may be going green so you can find the best solution to your problem.

About the Author

stefan schulzStefan Schulz is the founder and owner of PV Pool Cleaner. He spent his college years working at Niagara Pools and Spas, one of the largest Swimming Pool and Hot Tub Dealers in the Eastern United States.

Today, he utilizes his background, experience as a pool owner, and the resources of his digital marketing agency, Orpical Group, to generate informative and engaging content for pool owners everywhere.