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How to Keep Swimming Pool Water Clear

A swimming pool in Thailand

There are many advantages of having a swimming pool in one’s backyard. Aside from providing hours of fun and entertainment, a swimming pool also provides a means for low impact aerobic exercise (swimming) and other pool-based workout activities. A swimming pool beautifies one’s home, even adding to its market value. But maintaining a swimming pool is not a breeze.   Swimming pool water can quickly turn cloudy, hazy or green if ill-maintained.

Why does swimming pool water turn cloudy or green? Are there standards and easy-to-do solutions on how to keep swimming pool water clear?

Causes and Solutions for Cloudy or Green Pool Water

A Woman in a Swimming Pool

Lack of Chlorine

Even a well-maintained swimming pool can turn cloudy or green overnight. There are three common reasons why this happens. First, the free chlorine in the pool is depleted after constant, heavy use. Second, heavy rains will ultimately dilute the chlorine in an outdoor pool. And third, intense UV light can also deplete then pool’s free chlorine. Remember the diving, synchronized swimming and polo pools at the 2016 Rio Olympics? They turned emerald green because hydrogen peroxide, which is a de-chlorinator, was added to the pool’s water as part of maintenance.  Note that green pool water usually means algae in the water.

Solution: If the swimming pool water is cloudy or is green due to lack of free chlorine, the quickest solution is to shock the pool.  Shocking a pool means super-chlorinating the water. Factors such as the size of the pool, how green or cloudy the pool is, and even the type of filter are considerations. For pools with cartridge or sand filters, liquid chlorine is highly recommended. For a swimming pool that has a Diatomaceous Earth (DE) filter, granular chlorine is best.  Before shocking the pool water, its pH should be around 7.2 as its level will rise after shocking.

The pump should be on for at least 24 hours for the water to turn cloudy blue or blue. However, shocking the pool water will not clear up a cloudy or green pool if there is no pool filter. A clarifier solution need not be added if the pool is properly filtered. In some instances a flocking agent can be used to bind together small particles (algae) together, sink them to the bottom of the pool, then vacuumed up.

It is recommended to test and adjust the alkalinity and pH levels of the pool water 24 hours after shocking. The chlorine level would still be high, but this will stabilize after a few days.  For maintenance purposes and for crystal clear water, super chlorination the pool water weekly is recommended.

Imbalanced or Improper Pool Chemical

Maintaining the correct level of pool chemicals is a very important step in keeping the water clear and free from algae. Adding an incorrect amount or using the wrong chemical are two major causes of cloudy or green water.

Total alkalinity (TA) must also be monitored as high TA may cause calcium and pH scaling which in turn contribute to water cloudiness.

Accumulated bromine, phosphate and cyanuric acid (CYA) in high levels may contribute to pool water cloudiness. The free chlorine and CYA in the water must be balanced as high level of CYA reduces free chlorine.

Solution:  There are water testing kits available to efficiently and correctly measure the pH and chlorine levels of pool water. An ideal pH level should be between 7.2 and 7.6. If the swimming pool pH level is high, adding acid such as sodium bisulphate or muriatic acid to the water will lower it. If the pH level is low, adding alkali such as sodium carbonate will balance it. Total alkalinity must be between 80 ppm to 120 ppm to avoid scaling.

The ideal chlorine level is 3 parts per million (ppm). If the chlorine level is low, add chlorine. Chlorine stabilizer such as cyanuric acid will prevent depletion of chlorine due to UV exposure.  However, as mentioned earlier, too much CYA will leave the pool water cloudy and highly at risk of forming algae.

Poor Filtration and Water Circulation Systems toy ship swimming pool

If the pool’s filtration system is faulty, or if it is not running at least 8 hours a day, then the pool water is likely to be cloudy. The pool filtration system’s purpose is to continuously “filter” or clean pool water to make it crystal clear. Poor water circulation system will also cause improper water circulation, making the pool water stagnant and cloudy.

Solution: There are a few points that need to be exact for the filtration and water circulation systems to work well. First, the circulation system, including the pump size, should be in synch with the pool’s size and design. The return or eyeball fitting must point down so that the water at the pool’s bottom will circulate properly.

Ideally, the pool filtration system should be running on a 24/7 basis more so during heavy use for the water to be clear. However, home swimming pools that are not used heavily would thrive on 8-10 hours of filtration. Particles that could be blocking the filter should be removed. Blocked filters will not properly function. Regularly cleaning and backwashing the pool are required for clean and clear pool water. Replacing DE and cartridge pool filters should be done when needed.

Environmental Factors

People, structures, animals, birds, trees and other foliage, sun, rain, wind and other environmental factors can affect the clarity of pool water. Direct UV rays will deplete the pool’s free chlorine; but if trees or structures block direct sunlight, then free chlorine level will not be affected.

Rain (fresh water) can affect the free chlorine level of pool water. After heavy rains, it is best to test the chlorine level of the pool.

Pollen, blown foliage and other particles may land in the pool water. Sunblock and other body oil used by swimmers may accumulate in the pool, causing cloudiness.

Solution: Skim and vacuum the swimming pool as needed. It is best to use a cleaning net to skim the pool for particles, and empty the skimmer basket. It is best to use an efficient pool vacuum to clean the bottom of the pool on a regular basis.

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