Causes of Cloudy Pool Water and How to Beat It

There are three primary ways poor filtration manifests to create cloudy pool water. First, the filter may not be running the minimum of 8 to 10 hours daily, which causes stagnant and cloudy water. It may also be clogged or worn out, unable to do the job properly regardless of how long it runs. Finally, there could be a bacterial colony — biofilm —living in the filter and spreading through the pool. The simplest fix is a semiannual cleaning and replacement of the filters.

An imbalance of free and combined chlorine results in cloudiness. Free chlorine is the chlorine that hasn’t yet been used to sanitize the pool, while combined chlorine is what is actively sanitizing. When combined levels outpace free, algae or bacteria growth causes cloudiness or, in some cases, a milky appearance. Add enough chlorine to bring free levels to between 2 and 3 ppm.

Cyanuric acid, a conditioner, prevents ultraviolet rays from destroying free chlorine. However, too much conditioner can also be a problem, because the excess acid binds with chlorine, making the latter less effective at preventing the growth of microorganisms like algae. The only way to fix this is to replace a portion of the chlorinated water with natural water, until levels are more acceptable and cloudiness recedes.

There are a few ways heavy rain can lead to cloudy pool water. If you have plants next to your pool, the planters may overflow. That dirt contains phosphates and when it hits the water, it becomes a nice breeding ground for algae. Heavy rain also carries total dissolved solids, TDS, because rain absorbs all sorts of things before it hits the pool, including particulate matter, chemicals, and mites. TDS levels above 2500 mean cloudy pool water.

Water hardness refers to the levels of magnesium and calcium salts, which are measured by the saturation index or SI. When the SI is zero, pool water is balanced. At 0.5 or higher, calcium carbonate starts depositing on surfaces. When it scales, it imparts a grayish crust that clouds the water. The crust clogs filters, builds up in pipes, and leads to poor filtration and damaged equipment. Restoring balance requires adding the right levels of calcium chloride or  CaCl2.

Water’s ability to absorb and neutralize acid determines its total alkalinity and this is tied to pH. Water with a pH of 7.8 or higher will become cloudy. However, when it comes to total alkalinity, the carbonate hardness — not to be confused with calcium carbonate — is the determining factor. If total alkalinity is higher than 200 ppm, this means that chlorine is ineffective. The goal is to make sure than the carbonate hardness is high enough that pH doesn't fluctuate.

While there are plenty of chemical solutions for the myriad causes of cloudy pool water, there are a few natural ones, too. Baking soda is a natural carbonate, and if your pool pH is between 7.2 and 7.5, it will clear up the problem by raising its alkalinity.

First thing to do is to test the pH and alkalinity. If alkalinity is lower than 110 ppm, baking soda may help. For every 10,000 gallons, you’ll need about 1.5 pounds of baking soda to effectively raise alkalinity by 10 ppm. Throw the powder in and wait about 6 hours for it to dissolve before turning on the pump. Retest after another 6 to 10 hours and repeat the process if the numbers aren’t where they need to be.

One of the ways you can clean your pool without all of the chemicals is to turn it into a natural pool with the help of hydrogen peroxide. This powerful natural oxidizer prevents the growth of bacteria and algae by taking away their food source. For example, the biofilm that can accumulate in chlorinated pools won’t have the chance to make the pool cloudy. Hydrogen peroxide can also be used in chlorinated pools that don’t use diatomaceous earth pumps.

To change your pool, you’ll need protective gear and 35% food-grade hydrogen peroxide, which is 11 times more powerful than the commercial version available at the pharmacy. For every 250 gallons, add a cup of hydrogen peroxide. That means for a 10,000 gallon pool, you’ll need 40 cups. Run the pump for at least 6 hours and test. Hydrogen peroxide levels need to be between 50 and 90 ppm at all times, and filters need to be changed every other week.