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Understanding Pool Filter Types and How They Work

Pool filters come in three main types, each with different cleaning needs and maintenance schedules. Sand filters are the most common residential option, using layers of specially graded sand to trap debris and particles as water passes through. Cartridge filters use pleated fabric elements that catch debris on their surface, similar to an air filter in a car. Diatomaceous earth (DE) filters use a powder made from fossilized algae to create an extremely fine filtering surface that can catch very small particles.

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Each filter type works by forcing pool water through a filtering medium that traps dirt, leaves, algae, and other contaminants before returning clean water to your pool. Sand filters typically need backwashing when pressure builds up, cartridge filters need rinsing and occasional soaking, and DE filters need backwashing followed by recharging with fresh powder. Understanding your specific filter type is the first step toward maintaining it properly.

The size of your filter matters significantly. Filters are rated by gallons per minute (GPM) they can handle. A filter that's too small for your pool will struggle and require more frequent cleaning. Most residential pools use filters rated between 15 and 30 GPM, though larger pools may need higher-capacity units. You can find your filter's specifications on the tank itself or in your pool equipment manual.

Regular filter maintenance extends the life of your equipment and keeps your water clean and clear. Neglected filters become clogged, forcing your pump to work harder and use more electricity. Extremely dirty filters can fail suddenly, requiring expensive replacement. Understanding what type of filter you have and how it functions helps you recognize when it needs attention and what cleaning method to use.

Practical Takeaway: Locate your pool filter and identify which type you own. Check the equipment tag or manual for the model name and GPM rating. This information will guide all your future maintenance decisions.

Signs Your Pool Filter Needs Cleaning

Your pool filter will send you clear signals when it's time for cleaning. The most obvious sign is rising pressure on the filter's pressure gauge. Most filters operate normally at 10 to 20 PSI (pounds per square inch), though the exact range depends on your specific unit. When pressure climbs 8 to 10 PSI above the normal operating level, your filter is telling you it's becoming clogged with debris. This pressure reading is the most reliable indicator that cleaning is needed.

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Water clarity also tells you when your filter is struggling. If your pool water becomes cloudy or murky despite adequate chemical levels, or if you notice debris returning to the pool water, your filter isn't working effectively. Poor water circulation is another sign—if water doesn't flow smoothly from your return jets or circulation seems weak, a clogged filter may be restricting flow. Some pool owners notice their equipment running longer than usual to achieve normal filtration cycles.

The frequency of filter cleaning varies based on several factors. Heavy use, lots of trees nearby, frequent rain, and hot weather all increase debris in your pool. A pool in a busy household might need cleaning every 2 to 4 weeks during swimming season, while a lightly used pool in a protected location might go 6 to 8 weeks between cleanings. Swimming creates algae-promoting conditions and stirs up debris, increasing filter workload.

Different filter types show problems in different ways. Sand filters show rising pressure and require backwashing. Cartridge filters may not show high pressure but still reduce water flow, requiring a visual inspection and rinse. DE filters combine both issues—rising pressure and reduced flow. Checking your pressure gauge weekly during swimming season helps you establish a normal baseline and recognize when pressure creeps up.

Practical Takeaway: Check your filter's pressure gauge weekly during swimming season and note the normal operating pressure. When pressure rises 8 to 10 PSI above normal, schedule a cleaning. Keep a simple log of pressure readings to track patterns.

Cleaning Sand Filters: Step-by-Step Instructions

Sand filter cleaning is called "backwashing" because water flows backward through the filter to flush out trapped debris. The process typically takes 3 to 5 minutes and is straightforward once you understand the steps. Before starting, turn off your pump and pool equipment. Locate the multiport valve on top of your filter—this valve controls water flow direction and has several settings including Filter, Backwash, Rinse, and Waste.

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Begin by switching the multiport valve to the Backwash position. Open any air relief valve on top of the filter tank by turning it counterclockwise about half a turn. This allows air to escape. Now turn on your pump and let it run for 3 to 5 minutes. Watch the sight glass (the clear window on the side of most filters) or check the discharge water. When the water runs clear, you're done backwashing. Turn off the pump.

Next, move the multiport valve to the Rinse position. This sends water through the filter normally to settle the sand bed. Run the pump for about 30 seconds to 1 minute, watching the sight glass until water runs clear. Turn off the pump again. Finally, return the multiport valve to the Filter position. Close the air relief valve by turning it clockwise. Your filter is now ready to resume normal operation. Turn your pump back on and monitor pressure to confirm it has dropped to normal levels.

Some important details about sand filters: the sand bed typically lasts 3 to 5 years before it becomes worn and less effective at filtering. Hard water areas may experience calcium buildup that reduces filtering efficiency. If your filter doesn't respond to backwashing or pressure remains high, the sand may need professional cleaning with special acids, or the sand bed may need replacement. Sand filters occasionally get "air locked" where air bubbles prevent water flow—if this happens, open the air relief valve completely and restart the pump slowly.

Practical Takeaway: Practice backwashing your sand filter when pressure is only slightly elevated. This trains you to perform the task confidently when you need it. Mark your multiport valve settings with waterproof tape so you can quickly identify each position.

Cleaning Cartridge Filters: Detailed Methods

Cartridge filter cleaning is different from sand filter backwashing because cartridges cannot tolerate high-pressure water flow. Instead, cartridges are cleaned by rinsing them with a regular garden hose. First, turn off your pump and close the isolation valves on both sides of the filter if your system has them. This prevents water from draining from your pool. If you don't have isolation valves, be prepared for some water loss when you open the filter tank.

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Most cartridge filters have a large tank held together with a clamp band or bolts around the middle. Loosen this clamp by turning the band counterclockwise, or unscrew the bolts. As you open the tank, water will drain out—position a bucket or allow it to drain safely. Once open, you can lift out the cartridge element. If your filter has multiple cartridges, you may need to remove them one at a time or all at once depending on the design.

Rinse the cartridge thoroughly with a garden hose using medium water pressure. Start at the top and work downward, rinsing both the inside and outside surfaces. Pay special attention to the pleats (ridges) where debris accumulates. You should see dirty water spray out as you rinse. Continue until clean water flows from the cartridge with no visible dirt. This typically takes 5 to 10 minutes per cartridge. Never use a pressure washer, as the high pressure damages the pleated fabric.

For deeply soiled cartridges, soak them overnight in a bucket containing a mixture of pool filter cleaner and water. Many products are designed specifically for cartridge filters. After soaking, rinse again thoroughly with your garden hose. This process removes built-up oils and minerals that simple rinsing cannot remove. Replace the cartridge in the tank, close and tighten the tank seal, and reopen any isolation valves. Turn your pump back on and check for leaks around the tank seal. Most cartridge filters need cleaning every 4 to 6 weeks during heavy use, and cartridge elements typically last 1 to 3 years before replacement.

Practical Takeaway: Keep a dedicated bucket and cartridge cleaning solution in your pool equipment area. Clean your cartridges more frequently during heavy-use periods and always check for tears in the pleated fabric—damaged