Sand, Cartridge, or DE: How to Maintain Your Pool Filter
Your filter does the quiet, constant work of removing particles that make water cloudy. Chemistry kills contaminants; the filter takes them out. A neglected filter leads to cloudy water, higher chemical use, and extra strain on the pump. Fortunately, filter maintenance is straightforward once you know which type you have and how to read its pressure gauge.
Know your filter type
There are three common types of residential pool filters.
Sand filters push water through a bed of specially graded filter sand. They are simple, durable, and inexpensive to maintain. They filter a little less finely than the other types but work well for most pools.
Cartridge filters push water through pleated fabric cartridges. They filter finer particles than sand and do not require backwashing, which saves water. Instead, you remove and rinse the cartridges.
Diatomaceous earth, or DE, filters use grids or fingers coated with a fine powder made from fossilized organisms. DE filters provide the finest filtration of the three. They require backwashing and adding fresh DE powder afterward, along with periodic full teardown cleaning.
Learn to read the pressure gauge
The pressure gauge on top of your filter is your best maintenance tool. After cleaning the filter, with the pump running normally, note the pressure. That is your clean baseline. As the filter traps dirt, pressure rises. A common guideline is to clean the filter when the pressure climbs about 8 to 10 psi above the clean baseline, though your manufacturer's guidance comes first.
Do not clean the filter too often. A slightly dirty filter actually traps finer particles than a perfectly clean one, especially with sand. Clean when the gauge says to, not on a fixed schedule.
If the gauge seems stuck or reads zero while the pump runs, the gauge may be broken. Gauges are inexpensive to replace.
Backwashing a sand or DE filter
Backwashing reverses water flow through the filter to flush out trapped debris through a waste line. Always turn the pump off before moving the multiport or backwash valve; changing positions while it runs can damage the valve. Then set the valve to backwash, turn the pump on, and run it until the sight glass or waste water looks clear, usually a couple of minutes. Turn the pump off, set the valve to rinse if your filter has that setting, run briefly to resettle the media, then turn off and return the valve to filter.
Backwashing removes water, so top up the pool afterward. For a DE filter, add the correct amount of fresh DE through the skimmer after backwashing, as specified on the filter's label.
Be aware that backwash water contains pool chemicals. Check local rules about where it may be discharged.
Cleaning a cartridge filter
Turn off the pump and, ideally, the breaker. Open the air relief valve to release pressure before opening the tank. Remove the cartridges and rinse them with a garden hose, working from top to bottom and between the pleats. Avoid pressure washers, which can damage the fabric. A few times a season, or when rinsing no longer restores normal pressure, soak cartridges in a filter cleaning solution following the product instructions. Many owners keep a second set of cartridges so one can dry and be cleaned while the other is in use.
Deep cleaning and media replacement
Sand typically lasts several years, but over time the grains become rounded and filtration declines. Oily deposits and calcium can also cause channeling, where water finds paths through the sand without being filtered. If cleaning no longer helps and water stays dull, it may be time to replace the sand.
Cartridges wear out too. Signs include torn fabric, flattened pleats, cracked end caps, or very short intervals between cleanings.
DE filters should be fully disassembled and cleaned at least once or twice a year, inspecting grids for tears. If DE powder appears on the pool floor after backwashing, a grid may be torn.
Signs of trouble
Sand in the pool often means a broken lateral inside a sand filter. Pressure that rises extremely fast may mean the filter is overloaded with algae or debris, or that something like a clogged return is restricting flow. Pressure that stays very low may mean a restriction before the filter, such as a clogged pump basket.
Safety notes
Filters operate under pressure. Never open or loosen a filter tank, clamp, or lid while the pump is running, and always release air through the relief valve first. Damaged clamps or tank parts should be replaced, not ignored; a failing clamp can release with dangerous force.
A clean filter pays off
A well-maintained filter makes chemistry easier, keeps water sparkling, and reduces strain on your pump. A few minutes of attention to the pressure gauge each week is one of the best investments in your pool.