Why Did My Pool Water Turn Green After Using Calcium Hypochlorite?

green swimming pool water

. Possible Causes

1.Algae Growth:

Although calcium hypochlorite is a disinfectant, it doesn’t eliminate all types of organic matter instantly. If there are organic materials such as leaves, grass clippings, or other debris in the pool, these can provide nutrients for algae. This can lead to rapid algae growth, causing the water to turn green. Algae are microscopic plants that thrive in water and can multiply quickly under the right conditions, especially when the water is warm and there’s plenty of sunlight.

2.Metal Reactions:

If your pool water contains high levels of metals like copper or iron, adding calcium hypochlorite can cause these metals to react chemically. This reaction can result in green precipitates or dissolved metal ions, which can turn the water green. Metals can enter your pool water through various sources such as fill water, corroded pool equipment, or algaecides containing metals.

3.Excessive Calcium Hypochlorite:

Overuse of calcium hypochlorite can result in an excessively high chlorine level, disrupting the balance of the water and causing it to turn green. High chlorine levels can oxidize metals present in the water, leading to discoloration. Additionally, when the chlorine level is too high, it can bleach out the cyanuric acid (stabilizer) in the water, reducing its effectiveness and allowing the sun to burn off the chlorine more quickly, making it less effective at controlling algae and bacteria.

. Solutions

1.Test and Adjust Water Chemistry:

Use pool testing tools to check chlorine levels, pH, total alkalinity, and metal ion concentrations. Ensure all parameters are within the normal range. Maintaining proper water chemistry is crucial for preventing algae growth and metal reactions. Ideal levels are typically:

  • Chlorine: 1-3 ppm
  • pH: 7.2-7.6
  • Total Alkalinity: 80-120 ppm
  • Calcium Hardness: 200-400 ppm

2.Clean Organic Debris:

Use your filtration system or manually remove organic materials from the pool to prevent algae growth. Skimming the pool surface regularly and vacuuming the pool floor can help keep the water clean. It’s also a good idea to trim trees and bushes around the pool to minimize the amount of organic debris that falls into the water.

3.Use Algaecide:

If algae are the issue, applying an appropriate algaecide can help kill the algae and clear the water. There are different types of algaecides available, including copper-based, quaternary ammonium compounds, and polyquats. Choose one that’s suitable for your pool and follow the manufacturer’s instructions for use.

The swimming pool is covered with green algae

4.Metal Sequestrants:

If metal content is high, using a metal sequestrant can help bind the metals and prevent them from reacting with the chlorine. Metal sequestrants, also known as metal chelators, work by keeping metals in solution so they don’t precipitate out and cause staining or discoloration. Regular use of a metal sequestrant can help maintain clear water.

. Preventive Measures

1.Regular Maintenance:

Keep up with regular pool maintenance to prevent issues before they start. This includes testing the water weekly, cleaning the pool, and maintaining the proper chemical balance. Regular maintenance can help ensure that your pool stays clean, clear, and inviting.

2.Shock Treatment: 

Perform shock treatments as needed to keep the water clear. Shocking the pool involves adding a large dose of chlorine to kill off bacteria, algae, and other contaminants. It’s typically done every 1-2 weeks or after heavy use, heavy rain, or when the water starts to look cloudy. Be sure to follow the manufacturer’s instructions for shocking your pool.

3.Proper Storage of Chemicals: 

Store pool chemicals properly to prevent contamination and degradation. Keep them in a cool, dry place, away from direct sunlight and moisture. Always follow the manufacturer’s recommendations for storage and use.


By understanding these potential causes and implementing the appropriate solutions, you can effectively address and prevent your pool water from turning green after using calcium hypochlorite. Regular testing and maintenance, along with the right preventive measures, can help you avoid the green water problem and enjoy a crystal-clear pool.