How to clean a cartridge, sand, and DE pool filter
Clean the filter when running pressure is about 8–10 psi above the clean baseline, or when flow drops and the chemistry is fine. Rinse a cartridge, backwash sand, and backwash then recharge DE. Shut the pump off and release tank pressure before you open the lid.
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Shut the pump off before you open a filter. Release the air at the relief valve before you take the lid clamp off.
Start from the pressure gauge
Write down the pressure when the filter is clean and the pump is running at its normal speed. Clean the filter when the gauge sits about 8–10 psi above that number, or when flow at the returns drops and chemistry is otherwise fine. Cleaning on a calendar alone, while pressure is still normal, wears cartridges out faster than the dirt does.
Turn the pump off. Open the air relief and let the tank pressure fall before you loosen a clamp or a multiport. Opening a pressurized filter lid is how bands and lids get bent.
Cartridge filters
Hose the cartridge from the top down so dirt leaves the pleats instead of packing deeper into them. A nozzle is enough. A pressure washer cuts the fabric and the cartridge is then finished. Rinse until the water running out of the pleats is clear.
Replace the cartridge when the pleats stay gray and stiff, when the end caps are cracked, or when pressure climbs again within a few days of a thorough rinse. Match the replacement by the filter model and the cartridge length, not by a diameter you estimated. The measurements are in how to match a pool filter cartridge. A short cartridge in a tall tank leaves a path around the element and the pool never gets filtered.
Sand filters
Backwash until the sight glass runs clear, then rinse if the valve has a rinse position, and return the handle to filter. Do this with the pump running only in the positions the valve manual allows. Moving a multiport handle while the pump is on can break the spider gasket.
Sand is not permanent. When backwashing no longer brings the pressure back down, or the sand is several years old and channeling, replace the sand and the laterals if they are cracked. The laterals are the part people skip. Broken laterals send sand back to the pool.
DE filters
DE filters need a recharge after every backwash. Use the pounds of diatomaceous earth printed on the filter label, mixed into a slurry and poured slowly into the skimmer with the pump running. A heaping guess coats the grids unevenly. Too little DE lets dirt reach the fabric. Too much cakes the grids and spikes the pressure.
If pressure will not hold a normal interval between backwashes, the grids may be torn or caked with scale and oils. Hosing them is the first step. Soaking and replacing grids is a parts job tied to the filter model. Grids, clamps, and pressure gauges are in equipment. If the pump is also full of air, fix prime first. See why a pool pump loses prime.
Questions
When should I clean a pool filter?
When the gauge reads about 8–10 psi above the pressure you wrote down with a clean filter and the pump at its normal speed, or when return flow drops. Cleaning on a calendar while pressure is still normal wears a cartridge out faster.
How do cartridge, sand, and DE filters get cleaned?
A cartridge is rinsed. A sand filter is backwashed. A DE filter is backwashed and then recharged with fresh DE. The steps are not interchangeable. Shut the pump off and open the air relief before you loosen a clamp or a multiport.
What if filter pressure will not stay down after a cleaning?
On a DE filter, torn or scaled grids often will not hold a normal interval between backwashes. Grids, clamps, and gauges have to match the filter model. If the pump is also full of air, fix prime before you blame the grids.