Pool Filter Cleaning

Why filter pressure is the number to watch

Every filter has a clean starting pressure: the gauge reading right after its last cleaning. As dirt loads up, pressure rises and flow falls. Filter makers generally call for cleaning once the gauge reads about 8 to 10 psi above that clean starting point, though the exact trigger is in your filter's manual. Run much past that and circulation drops, chlorine has to work harder, and the pump strains.

Cleaning too often has a cost too. Most filters trap fine particles a little better once a thin layer of dirt has built up on the media, so hosing it off at the first small rise in pressure throws away some of its polishing ability. Before opening anything, we confirm the high reading is coming from the filter and not from a partly closed valve or a blocked return. If something inside is broken, that becomes a filter repair, not a cleaning.

How each filter type gets cleaned

Every cleaning starts the same way: pump off, air relief valve open, and nothing loosened until the gauge sits at zero. A tank that still holds pressure can throw its lid or clamp the moment it is opened, so that step is never rushed. After that, the work depends on what kind of filter you have.

• Cartridge filters: each cartridge comes out and is rinsed pleat by pleat, top to bottom, with a garden hose spray nozzle. Cartridges that stay greasy or stiff with mineral get a soak in a filter cleaning solution before the final rinse.
• DE filters: backwashing alone leaves oils and old powder caked on the grids. A full cleaning means removing the grid assembly, rinsing each grid, checking the fabric for tears, reassembling, and recharging fresh DE through the skimmer in the amount your filter calls for. DE is a fine powder, so it is handled with a dust mask.
• Sand filters: the pump is turned off before every valve change, then the filter is backwashed until the sight glass or waste line runs clear, followed by a short rinse to resettle the bed. When the bed cakes or forms channels, water slips past it unfiltered and backwashing stops bringing the pressure down. At that point the sand itself is replaced.

Houston debris and your filter

Filters here work hard. Spring brings oak catkins and pollen that slip past skimmer baskets and coat cartridges with a yellow-green film, and live oaks drop their old leaves in spring rather than fall. Heavy rain washes mulch, soil, and lawn clippings over the coping; at Houston Intercontinental, June is the wettest month on average, with October and May close behind. The long, hot season also means dead algae lands in the filter every time the pool is shocked.

After a storm or a green pool cleanup, a filter can load up in days instead of weeks. Dead algae and fine sediment pack into cartridge pleats and DE grids quickly, so a recovery usually takes more than one cleaning. Freshly replastered pools are similar: plaster dust can shorten filter runs for a while, which is normal.

What to expect after a cleaning

When the filter goes back together, we leave the air relief valve open until water comes out, restart the pump, and write down the new clean pressure. That number becomes the baseline for the next cleaning. Water clarity usually improves over the next day or so as the filter catches up.

If you are on weekly pool service, the gauge gets read on every visit and cleanings are scheduled by pressure rather than a fixed calendar. During pollen season and after storms that means more often; in the cooler months, less. Either way you get a note after the visit saying what was done and what the gauge read.

Signs your filter is due

• The gauge reads 8 to 10 psi or more above its clean starting pressure
• Weak return jets or a pool cleaner that barely moves
• Cloudy water even though chlorine and pH test fine
• Backwashing no longer brings the pressure down
• A yellow-green film on the cartridges after spring pollen
• Water that will not clear after shocking an algae bloom

What we handle

• Cartridge rinsing and deep-clean soaks
• DE grid teardown, inspection, and recharge
• Sand filter backwash and rinse
• Sand bed checks and sand replacement
• Pressure gauge and air relief valve checks
• Tank o-ring inspection on reassembly
• Extra cleanings after storms and algae cleanups
• A recorded clean pressure for next time