Pool Filters: Sand, Cartridge and DE

Applies to: In-ground and above-ground home pools with sand, cartridge or diatomaceous earth (DE) filters

What the filter does

Hayward says clear pool water takes both adequate filtration and proper water chemistry. ENERGY STAR advises cleaning or backwashing the filter as the manufacturer recommends, noting that some designs never need backwashing, so check your manual.^[1][6]

Reading the pressure gauge

Hayward's ProSeries sand filter manual says to note the gauge reading when the filter is clean, then backwash when the reading has risen by the amount the manual gives. Hayward's SwimClear cartridge manual likewise says to clean or replace the cartridge when pressure rises a set amount above the starting pressure, or when flow drops below the desired filtration rate.^[1][2]

Not every manual works this way. Bestway's manual for one above-ground sand filter pump gives a single reading at which to clean, and calls its gauge a reference, not a precision instrument. Follow your own filter's manual.^[4]

Hayward says a gauge that never moves, pump on or off, is broken. If pressure stays high, it lists algae clogging the filter (filters cannot kill algae), a pump too big for the filter, or a blocked return line.^[7][8]

Sand filters: backwash and rinse

Hayward explains that sand traps dirt as water passes through. When trapped dirt slows the flow, it is time to backwash: the valve reverses flow up through the sand and flushes dirt out the waste line.^[1][9]

Hayward's sequence for its ProSeries filters is below. Check your own valve and manual:^[1]

1. Turn the pump off. Hayward says never to change the valve position while the pump is running.^[1]
2. Set the valve to Backwash, start the pump, and run it until the water in the sight glass is clear.^[1]
3. Turn the pump off, set the valve to Rinse, and run briefly. Hayward says this sends dirty backwash water to waste instead of back to the pool.^[1][10]
4. Turn the pump off, set the valve back to Filter, and restart.^[1]

Hayward notes that a new or very dirty pool may need frequent backwashing at first. For one above-ground sand filter pump, Bestway says the unit must be switched off and unplugged before any maintenance.^[1][4]

Cartridge filters: remove and rinse

Hayward's SwimClear cartridge manual gives these steps:^[2]

1. Shut off the pump and turn off its power (Hayward says to turn off power before working on the pump). If the filter sits below water level, close valves to prevent backflow.^[2][11]
2. Remove the drain plug and open the manual air relief valve to drain the filter.^[2]
3. Release the safety latch, unscrew the lock ring and lift out the cartridge.^[2]
4. Hose the cartridge inside and out. Do not pressure wash it, which can damage the element.^[2]
5. Reinstall it and tighten the lock ring until the safety latch fully engages. Before restarting, Hayward says all suction and discharge valves must be open, and to stand clear of the filter. Follow your filter manual's start-up steps.^[2]

For suntan and body oils, Hayward suggests a filter element cleaner used per its directions, in a plastic container, with extreme care, because cleaning agents can harm eyes, skin and clothing.^[2]

DE filters: backwash and recharge

In a DE filter, diatomaceous earth forms a coating on fabric-covered filter elements. Hayward says this lets the filter catch microscopic particles, and that when the DE's dirt-holding capacity is reached it is time to backwash.^[3][14]

Hayward's ProGrid DE manual describes this cycle:^[3]

1. Shut off the pump, set the valve to Backwash, restart, and backwash until the waste water runs clean.^[3]
2. Shut off the pump and return the valve to Filter as your manual directs.^[3]
3. Add a fresh charge of DE through the skimmer with the pump running, using the amount on your filter's label.^[3][15][16]
4. Record the new gauge reading. This is your clean pressure.^[3]

Hayward warns not to run its grid filter for more than a minute or two without the DE pre-coat. It says backwashing does not remove all the DE: the only way is to take the filter apart, and the filter should be taken apart and cleaned at least once a year. Its ProGrid manual says the filter should be serviced only by a qualified professional, so ask one about this job.^[3][15]

Tank lids, clamps and air relief valves

• Hayward says all suction and discharge valves must be open when starting the system, and to stand clear of the filter.^[2]
• Close the air relief valve only when a steady stream of water comes out, per Hayward.^[2]
• Hayward warns never to operate or test the circulation system above the pressure limit in its manual, and never to purge the system with compressed air.^[1][11]
• Hayward says never to rely on hand-tightening its DE filter clamp, and to aim air relief discharge away from electrical devices.^[3]
• Hayward says equipment must be placed so young children cannot climb it to reach the pool.^[1]

When to call a professional