What Causes A Green Pool?

Green Pool Problems?

Poolwerx has always maintained that most swimming pool issues boil down to either water chemistry or filtration and circulation. A green pool is no different.

Big green pool

1. Chemistry Issues

More often than not, a swimming pool starts turning green due to a lack of chlorine. The free chlorine level should be maintained between 2.0 and 3.0 parts per million. The pool water should be tested at least once or twice a week to ensure that the level of chlorine is maintained at the recommended level. Find a Poolwerx location to have your water tested for free.

In addition, the pool water should be shocked routinely with granular chlorine (calcium hypochlorite) in most cases. We recommend at least once every two weeks, or more often in the heat of the summer. A shock treatment will raise the chlorine level very high for a short period of time, killing bacteria and waste, and making all the chlorine in the pool free and available to sanitize the pool water.

pH will also have an effect. If the pH is high, your chlorine is slow to react, and algae can begin to form, making the pool appear green or cloudy. If the pH is low, the chlorine will be “hyperactive”, reacting quickly, and dissipating out of the pool too rapidly, causing a low chlorine residual.

If the Stabilizer (Cyanuric Acid) level is too high, the chlorine also reacts very slowly, is less effective at killing bacteria and algae, and will actually stay in the pool too long, leading to high chlorine levels that cannot clear the green color out of the pool. This situation normally indicates a need to get your pool water analyzed by a swimming pool professional. Take a quart sample of the pool water into one of our locations for a computerized water analysis, and help with clearing the green color out of your pool.

Poolwerx van man testing water

2. Filtration Issues

If the swimming pool filtration system is performing poorly, or not running enough hours, the debris that the filter would normally filter out can remain in the pool water, causing the sunlight to refract through the pool water, giving it a greenish tint. Let’s look at the various filter types, and what you may need to look for when the pool looks green.

Sand filters are known for the lowest maintenance required. You do need to backwash the filter but you do not have to change your sand/glass media for years to come. Sand filters just take longer for it to filter out the fine debris. The sand can “channel”, the backwash valve gasket or O-ring can go bad, allowing the debris to bypass the filter and shoot back into the pool. The laterals beneath the sand can crack and allow the sand from the filter into the pool, making it even harder to turn the pool around.

Diatomaceous Earth filters take care of a very small particle, and can turn around a green or cloudy pool quickly. You should always check your pool return jets when adding DE to the skimmer to see if the DE is going through the filter and shooting into the pool. This indicates a filter issue that needs repair. If the filter pressure is building up very quickly it indicates a need to take apart and manually clean the filter, or that you may not be using the proper amount of DE.

Cartridge filters can take care of a pretty small particles as well, and normally clear a green cloudy pool fairly quickly. They normally last a year or two, and then can no longer do the filtering job. As the filter filters out debris, the pressure on the gauge will rise and the flow through the pool is reduced. If you have a green or cloudy pool and the pressure does not rise, it indicates that the debris is passing through the filter and back into the pool. This would keep the water green and cloudy, and would indicate a need to check the filter out.

If you’re encountering issues with your pool and need help, give us a call or bring us a sample of water, we can help you get it back to a sparkling blue in no time!

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