Causes Of Green Swimming Pool Water

Green coloration in swimming pool water is no doubted a sign of dirty water. As soon as the color of pool water changes to green, it turns from a refreshing to an annoying atmosphere for the viewers. This is the time when you need to worry about your pool. There are many factors responsible for the discoloration of swimming pool water, but it mainly occurs due to the imbalance ratio of chemicals. Some of the causes of the green swimming pool water are explained below:

1. Imbalanced Level of Chlorine

The most common cause of green swimming pool water is the uneven proportion of chlorine in the pool. The required amount of free chlorine in the pool is between 2 ppm to 4 ppm. If a sufficient amount of chlorine is not added or is less than 2 ppm, then the algae will start growing and turn the whole pool water green in a single day. Although chlorine is essential to add in the pool for the purification of water and to prevent mosquitoes and insects, if more than the required amount (4ppm) is added, it will turn the swimming pool into another greener shade.

2. High Level of Phosphate

Another cause for the discoloration of swimming pool water is the presence of high levels of phosphates in the water. These high amounts of phosphates are present in the pool due to the runoff of cleaner and fertilizer. As soon as the phosphate level reaches 500 ppb it is considered to be in the range of a high amount. These excessive phosphates are a great source of food for algae and a pool with a lot of phosphates is considered as their buffet. These algae will grow and change the color of swimming pool water to the green.

3. Inappropriate Level of pH

An improper level of pH is also one of the causes for the green color appearance of swimming pool water. The pH value of water shows either the pool water is acidic or basic. The desired level of pH is between 7.2 to 7.8 for swimming pool water. In case of a low value of pH, which is less than 7.2, the metal and plastic erosion will occur due to the acidic nature of water that will lead to the discoloration of water. If the pH value is greater than 7.8 then it will build scales of different elements including calcium and the basic nature of water will not be able to kill the bacteria. These bacteria further flourish to cause the water of the swimming pool to be green. 

4. Improper Filtration

The green color of swimming pool water can also occur due to the improper filtration system. The filter system removes out the algae, debris, and other dirt from the pool water through suction. If you are not running your filter for enough time or your filter is clogged and not working properly due to any maintenance fault, then it will not remove all the organic debris and algae from the swimming pool. Your pool water will remain stagnant and become a source of breed for the fungi and algae, causing the pool water to turn green.

5. Overgrowth of Algae

Overgrowth of algae is another factor accountable for turning the color of swimming pool water green. The growth of algae occurs due to the imbalance of chemicals and improper circulation of water.

They also grow rapidly in warm and humid weather. These reasons flourish the growth of algae and bacteria and make the pool water hazardous, cloudy and green.

6. Presence of Pollen

The presence of pollen in the pool is also a reason for the green swimming pool water. The pollen comes from the trees and plants present near the pool. They enter into the pool water through the wind. Pollens are difficult to filter out due to their tiny size so their amount starts to build up in the pool. This can change the water color to green or sometimes in the shade of greenish-yellow, but the good thing is that the color change due to pollen is harmless.  

7. Presence of Metals

Metals are also responsible for the change in the swimming pool water color to green. The elements of metal can be present in the pool from different sources which include the ladders, parts of pumps, copper heater, acidic nature of water, low-quality algaecides, and many more.  When you shock the pool, the particles of metal will get oxidize and the chemical imbalance will occur which changes the color of swimming pool water. If it is not treated, the surface of the pool will be stained, most probably permanently. This can also change the hair color of people who swims in this excessive metal water, from blonde to green.

8. Excessive Amount of Cyanuric Acid

Cyanuric Acid (CYA) is a stabilizer and conditioner used to prevent the degradation of chlorine during sunlight and its required amount is between 30 ppm to 50 ppm. The presence of CYA below or above the required values can be a reason for the green pool water. If the amount of CYA becomes too low, the chlorine will burn due to the ultraviolet radiation of sunlight. The excessive amount of CYA leads to an increase in the amount of chlorine in the swimming pool water. If the CYA amount reaches between 80 ppm to 100 ppm, the chlorine will become less active to kill algae and bacteria. The algae further grow to cause more green coloration to the pool water.


In this article, we have discussed the major causes for the green appearance of swimming pool water so you could know how to troubleshoot the issues. By knowing these causes you can be able to take care of your pool before it gets green. For saving your time from scrubbing and curing, and avoiding pool water discoloration, try your best to prevent the chemical imbalance by regularly testing pool water.