How to Tell if Your Sand Filter Sand Is Bad and Causing Cloudy Water

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Sand filters should keep your swimming pool water clear.
Image Credit: KatarzynaBialasiewicz/iStock/GettyImages

The sparkling clear water of your swimming pool makes it inviting on hot summer days. When the water slowly grows cloudy, you might ask if your sand filter sand has failed. There are several possibilities to consider when the pool water is cloudy, including a little basic maintenance on the filter system.


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About Sand Filters

Sand filters are pressurized filtering systems. The pool water is pumped through the sand, which filters out large particles as well as leaves, insects and debris. The larger particles increase the ability of the filter to remove smaller particles from the water. The clean water then returns to the pool. The filtration system should filter all of the water in the pool at least two or more times every 24 hours.

Though not all of the smaller particles may be filtered through the sand, each cycle captures additional particles that are even as small as 20 to 100 microns. After a few weeks, the dirt and debris will build up pressure in the filter tank by eight to 10 pounds. At that point, the filter should be backwashed or flushed clean of the debris.


Set the pump on the backwash setting to pull pool water back through the filter. The dirty water and debris drains out of a backwash hose, which cleans the sand in the filter.

Sand Filter Helper and More

To increase the efficiency of the filter, you can add a sand filter helper product on top of the sand in the canister. The product helps improve the pool water clarity by increasing the filter efficiency in capturing finer particles. Generally, a sand filter helper is added after backwashing.


In addition to the filter, clear water depends on sanitation. Chlorine kills algae and bacteria, which can also cloud the water and turn it green over time. Always test the chlorine level in the water, and if it has less than 1 ppm (part per million), simply add more chlorine. If more chlorine doesn't clear the water, you can "shock" the pool, but it may stay cloudy until all the water in the pool has passed through the sand filter several times, and you may have to backwash the filter before running a few more cycles to finish clearing the dead algae.

When adding chlorine doesn't work or the chlorine level is above 2 ppm, check the pH level. High pH, alkalinity and/or calcium levels reduce the ability of the water to hold fine particles in suspension and make the water look cloudy. Add pool chemicals formulated to reduce pH and alkalinity to bring the water back into balance. Run the filter for 12 to 24 hours and test the chemical levels again. The levels should be between 1 and 3 ppm chlorine, 7.2 and 7.6 pH, 90 and 120 ppm alkalinity and 200 and 350 ppm calcium.


Old Sand Loses Its Effectiveness

If the other measures don't work, add a clarifier and run the pump for 24 to 48 hours. If the water clears, then set the pump to run 12 hours during the day to keep the water circulating and to prevent cloudiness.

Whether a Hayward, Waterways or Triton sand filter, troubleshooting all other factors comes first. If nothing works, the sand in the filter may be to blame for the cloudy water. After five to seven years, the sand gradually loses its sharp edges and its ability to filter the water. When the sand no longer effectively filters the water, you should change it according to the instructions for your brand.


Put on protective gear, including a mask, safety goggles and gloves before removing the old sand and adding new sand to the filter. Any sand labeled as "pool sand" or "filter sand" will work since all sand-filter sand is sized the same – number 20 silica sand with 45 to 55 mm grains. After replacing the sand, backwash and then run the pump for several cycles to clean the pool water.