Pool Filter Cleaning and Maintenance: Sand, DE, and Cartridge

Your pool filter is running constantly during swim season, trapping everything from sunscreen and body oils to debris and algae. When it gets clogged, flow drops, water gets cloudy, and equipment strains. Here's how to maintain each type properly.

Which Filter Type Do You Have?

Before cleaning, identify your filter type. This determines the cleaning method entirely:

DE filters produce the clearest water by a significant margin — 3–5 microns catches particles that are invisible to the naked eye. Sand filters are the most common and lowest maintenance. Cartridge filters are popular for above-ground pools and smaller inground pools because they don't waste water during cleaning.

Sand Filter Maintenance

Sand filters are cleaned by backwashing — reversing water flow through the tank to flush out trapped debris. Your pressure gauge tells you when to backwash: when pressure reads 8–10 psi above your clean starting pressure (usually 18–25 psi at clean, so backwash at 26–35 psi).

How to Backwash a Sand Filter

1. Turn off the pump
2. Set the multiport valve to BACKWASH
3. Turn the pump on and run for 2–3 minutes, or until water runs clear in the sight glass
4. Turn the pump off, set valve to RINSE
5. Run for 30 seconds (this settles the sand and prevents bypassing)
6. Turn pump off, return valve to FILTER, restart pump

Never rotate the multiport valve while the pump is running — this damages the valve gaskets.

Deep Cleaning Sand Filters

Backwashing removes debris but not oils, sunscreen, and biofilm that coat the sand grains over time. These reduce filtration effectiveness even when pressure looks normal.

Once a season (or when water stays cloudy despite clear chemistry), use a filter cleaner/degreaser:

1. With the pump running on FILTER, pour the appropriate dose of sand filter cleaner into the skimmer
2. Let it circulate for the time specified on the product label (typically 8–12 hours)
3. Backwash thoroughly afterward

When to Replace Sand

Pool filter sand should be replaced every 5–7 years. Signs it's time: cloudy water that won't clear despite normal chemistry, sand returning to the pool through the return jets (broken lateral), or if you've never replaced it and it's been 7+ years.

Many technicians now recommend glass media instead of sand when replacing. ZeoSand (zeolite) and glass media filter down to 5 microns compared to sand's 20 microns, and they last longer. Cost difference is roughly $100–$200 more but performance improves significantly.

Diatomaceous Earth (DE) Filter Maintenance

DE filters are the highest-performing option but require more maintenance. They use a powder made from fossilized diatoms that coats internal fabric grids, creating an extremely fine filtration surface.

Backwashing a DE Filter

DE filters backwash similarly to sand filters, but you must add fresh DE after every backwash — the powder flushes out with the debris.

1. Backwash the same way as a sand filter (BACKWASH for 2–3 minutes, RINSE for 30 seconds)
2. After returning to FILTER, add fresh DE through the skimmer with the pump running
3. Amount: check your filter's label for the full DE charge (typically 1–6 lbs), then add 80% of that amount after backwashing (some DE remains on the grids)

Never run a DE filter without DE on the grids — the grids will clog with debris and require disassembly to clean.

Annual DE Filter Disassembly and Cleaning

Once per year (usually at pool opening or closing), DE filters need full disassembly:

1. Backwash first, then shut off the pump and relieve pressure
2. Open the filter tank — most have a clamp band or bolted collar
3. Remove the grid assembly
4. Spray each grid with a garden hose to remove remaining DE
5. Soak grids in a DE filter cleaner solution for 8–12 hours (or overnight)
6. Rinse thoroughly, inspect for tears in the fabric
7. Reassemble, add a full DE charge

Check each grid for tears, rips, or collapsed fabric. A torn grid allows DE (and debris) to bypass into the pool. Replacement grids run $20–$60 each depending on filter model.

Cartridge Filter Maintenance

Cartridge filters don't backwash — you remove the cartridge and rinse it. This uses less water but requires more hands-on maintenance.

How to Clean a Cartridge Filter

1. Turn off the pump and release air pressure from the filter's air relief valve
2. Open the filter housing (usually a top-mounted clamp or collar)
3. Remove the cartridge(s)
4. Rinse with a garden hose using a firm spray, working top to bottom between each pleat — do not use a pressure washer (it damages the pleats)
5. For deep cleaning: soak in a filter cleaning solution or a 10:1 water/muriatic acid solution for 1 hour, then rinse thoroughly
6. Allow to dry if possible before reinstalling (improves filtering surface), or reinstall immediately if needed
7. Replace O-rings with fresh lube annually

Cartridge Cleaning Frequency

Clean when pressure rises 8–10 psi above starting pressure, or:

• Every 1–2 months during heavy swim season
• After a big swim party or algae treatment
• At pool opening and closing

Having a spare cartridge on hand lets you swap them out and clean the dirty one without downtime.

When to Replace Cartridges

Cartridges last 1–3 seasons with proper care. Replace when:

• Pleats are collapsed, torn, or fraying
• The end caps are cracked or the fabric is separating
• Pressure remains high even after cleaning
• Water clarity doesn't improve after a fresh clean

Cartridge replacement cost: $25–$150 depending on filter model. Buying two at once so you always have a clean backup is worth it.

Pressure Gauge: Your Most Important Maintenance Tool

Whatever filter type you have, the pressure gauge is your indicator. Record the "clean" pressure when you start with fresh media or a clean filter. Write it on a piece of tape stuck to the filter housing. The 8–10 psi rise rule applies to all filter types.

If your pressure is perpetually at the high end despite cleaning, check for:

• Closed or partially closed return valves
• Debris in the pump strainer basket
• Clogged impeller on the pump
• Filter media that needs replacement (not just cleaning)

If pressure is consistently low (below normal starting pressure), that's a different problem — usually a water leak, air leak in the suction line, or a pump that's losing prime. Low pressure means less water is moving through the filter, not that the filter is clean.

For help diagnosing filter issues or if you're not sure your filter is performing correctly, our pool equipment repair guide covers repair costs and when to call a pro. You can also find pool service companies near you at poolservicemap.com for professional filter cleaning and inspection.