Your pool filter is the unsung hero of water clarity. It runs for hours every day, quietly trapping dirt, debris, dead algae, sunscreen, body oils, and the fine dust that Fresno's Central Valley is famous for. But a dirty filter can't do its job — and in Fresno's harsh conditions, filters get dirty faster than in most places.
The Three Types of Pool Filters
| Filter Type | Filtration Size | Common in Fresno? | Maintenance Frequency |
|---|---|---|---|
| Cartridge | 10-15 microns | Very common (newer pools) | Clean every 2-4 weeks |
| Sand | 20-40 microns | Common (older pools) | Backwash every 1-2 weeks |
| DE (Diatomaceous Earth) | 3-5 microns | Less common | Backwash monthly, full clean 2x/year |
Cartridge Filter Cleaning
Cartridge filters are the most popular choice in newer Fresno pool installations because they don't require backwashing (saving water in drought-prone California) and provide excellent filtration.
When to Clean
Watch your filter pressure gauge. When pressure rises 8-10 psi above the clean starting pressure, it's time to clean. In Fresno's summer, this typically means every 2-3 weeks. After dust storms, you may need to clean weekly.
How to Clean a Cartridge Filter
- Turn off the pump. Open the air relief valve on top of the filter tank
- Remove the tank lid and carefully pull out the cartridge(s)
- Hose down each cartridge with a strong spray nozzle. Work from top to bottom, spraying between each pleat. Rotate the cartridge as you go
- Inspect the cartridge for tears, worn end caps, or flattened pleats
- Reinstall and close the tank. Open the air relief valve, start the pump, and close the relief valve once water sprays from it
Deep clean quarterly: Soak cartridges overnight in a filter cleaning solution to dissolve oils and calcium buildup. Fresno's hard water deposits calcium on filter media faster than soft-water areas.
When to Replace Cartridge Filters
- Pleats are frayed, torn, or flattened
- End caps are cracked
- Cleaning no longer reduces pressure
- Filter is more than 2-3 years old with heavy use
Sand Filter Maintenance
Sand filters are simpler but less precise. Water flows through a bed of special filter sand that traps particles. They're common in older Fresno pools and are easy to maintain.
Backwashing a Sand Filter
- Turn off the pump
- Set the multiport valve to "Backwash"
- Turn the pump on and run until the sight glass shows clear water (usually 2-3 minutes)
- Turn off the pump
- Set the valve to "Rinse" and run for 30 seconds
- Turn off the pump and set back to "Filter"
Backwash when pressure rises 8-10 psi above baseline, typically every 1-2 weeks in summer.
When to Replace Sand
Filter sand should be replaced every 5-7 years. Signs it's time: water clarity declines despite proper chemistry, or you can feel the sand has become smooth and rounded (it should feel gritty). In Fresno's hard water, calcium can cause sand to clump — a condition called "channeling" where water flows through gaps instead of being filtered.
DE Filter Maintenance
DE (diatomaceous earth) filters provide the finest filtration of any pool filter type. They use a powder made from fossilized diatoms coated on internal grids.
Backwashing a DE Filter
- Backwash using the same process as a sand filter
- After backwashing, add fresh DE powder through the skimmer while the pump runs
- Use the amount specified by your filter manufacturer (typically 1 lb per 10 sq ft of filter area)
Full Teardown Clean (Twice Per Year)
Twice a year, open the filter tank, remove the grid assembly, and hose down each grid individually. Soak in a filter cleaner to remove oils and calcium. Inspect grids for tears — a torn grid means DE powder goes back into your pool.
Fresno-Specific Filter Tips
- Hard water scaling: Soak cartridges or grids in a 10:1 water-to-muriatic-acid solution annually to dissolve calcium deposits
- Dust storms: Clean filters immediately after major dust events — fine valley dust clogs filters rapidly
- Summer heat: Expect to clean filters 50% more frequently June through September. Higher pump run times and heavy bather loads mean more debris
- Agricultural fallout: Central Valley crop spraying and harvest dust can introduce fine particles your filter picks up. Clean more often during harvest season (late summer/fall)
The Cost of Neglecting Your Filter
A dirty filter doesn't just mean cloudy water. It forces your pump to work harder (higher pressure = higher electricity costs), reduces water flow (poor circulation = algae growth), and can eventually damage the pump motor. In Fresno's long, hot pool season, keeping your filter clean is the single most impactful maintenance task you can do.
Set a calendar reminder. Clean your filter on schedule, and you'll spend a lot less time and money fighting water problems all season long.