A sand filter uses a large tank filled with specialized silica sand to keep pool water clean and hygienic. As water is pushed through the sand bed, the sharp edges of the grains trap debris, dirt, and microscopic particles. Filtered water then returns to the pool. Regular cleaning is necessary because the accumulation of trapped particles eventually clogs the sand bed, impairing the filter’s performance and straining the circulation system.
Recognizing When the Filter Needs Cleaning
The primary indicator that a sand filter needs cleaning is a change in system pressure, monitored by the gauge on the filter tank. As the sand bed collects debris, resistance to water flow increases, causing the pressure inside the tank to rise. This rise, known as the “delta P,” signals a dirty filter. Backwashing should occur when the reading is 8 to 10 pounds per square inch (psi) above the clean operating pressure.
The clean operating pressure is the reading recorded immediately after a thorough cleaning. Ignoring high pressure forces the pump to work harder, leading to increased energy consumption and potential damage to components. Other signs of a clogged filter include a noticeable reduction in flow rate, such as sluggish water returns or ineffective skimming. Cloudy or murky pool water also suggests the filter is no longer effectively removing contaminants.
Step-by-Step Backwashing Procedure
Backwashing cleans the sand filter by reversing the direction of water flow to lift and flush trapped debris out of the sand bed. First, shut off the pool pump completely to protect internal components and the multi-port valve. With the pump off, set the multi-port valve handle to the “BACKWASH” position to divert the water flow.
Ensure the backwash hose is positioned to drain safely, then turn the pump back on to begin the cleaning cycle. Water flows up through the sand, dislodging debris and sending the dirty water out through the waste port. Continue backwashing for three to five minutes, or until the water visible in the filter’s sight glass runs completely clear.
Once the water is clear, shut off the pump before moving the valve, as changing the setting while running can damage the internal gasket. Move the valve to the “RINSE” position and turn the pump on for 30 to 60 seconds. This cycle settles the sand bed back into its correct configuration for optimal filtration. Skipping the rinse step can cause fine debris to blow back into the pool. Finally, turn the pump off, set the valve back to the “FILTER” position, and restart the pump to resume regular filtration.
Performing a Chemical Deep Clean
While routine backwashing removes loose debris, it cannot dislodge stubborn contaminants that accumulate deep within the sand bed. Over time, substances like oils, grease, and mineral scaling coat the sand grains, a condition known as “cementing” or “channeling.” This coating severely reduces the sand’s ability to trap particles and makes the filter media less efficient.
A chemical deep clean dissolves these trapped organic and mineral deposits. It is recommended at least once or twice a year, or when normal backwashing fails to restore the clean operating pressure. The process begins by backwashing the filter to remove loose debris.
Deep Cleaning Steps
Turn the pump off and set the valve to the “FILTER” position.
Introduce a specialized sand filter cleaner or mild acid solution into the system, typically by pouring it into the pump’s strainer basket.
Run the pump briefly to circulate the cleaner into the filter tank, then immediately shut it off.
Allow the chemical solution to soak and break down the deposits for eight to twelve hours.
Perform a second, extended backwash cycle to completely flush the chemical residue and dissolved contaminants to waste.
Extreme caution must be exercised when handling chemical cleaners. Ensure all chemical traces are fully rinsed out before the pool is used again.
Essential Post-Cleaning Maintenance
Once backwashing and rinsing are complete, immediately record the new pressure reading while the filter is operating in the “FILTER” position. This baseline pressure is the figure against which future increases will be measured, signaling the next required backwash. Recording this clean pressure helps prevent unnecessary backwashing, which wastes water.
Periodically inspect the multi-port valve as part of long-term care. The rubber O-rings and gaskets inside the valve maintain a proper seal and ensure correct water flow. Applying a silicone-based lubricant to the O-rings helps the valve handle move smoothly and prevents seals from drying out or cracking. If filter performance remains poor, check the sand media itself for signs of clumping or channeling.