How to Choose a Pool Filter - Sand, Cartridge, or DE?

The Three Pool Filter Types at a Glance

Every pool needs a filter. The filter’s job is to trap particles - algae, dirt, skin cells, sunscreen residue - and return clean water to the pool. Three technologies accomplish this, each with different filtration fineness, maintenance requirements, and costs.

The right choice depends on your pool size, local drain rules, how much time you want to spend on maintenance, and your water clarity expectations. This guide breaks down every factor. For a head-to-head technical breakdown, see the full comparison of DE vs. sand vs. cartridge filters.

Sand Filters - Easiest to Maintain

Sand filters push pool water down through a tank filled with graded silica sand (#20 grade, meaning grains 0.45-0.55 mm in size). Particles 20 microns and larger get trapped between sand grains; filtered water exits through a set of lateral tubes at the bottom of the tank and returns to the pool.

How backwashing works: When the filter gets dirty, you flip the multiport valve from FILTER to BACKWASH. This reverses flow through the tank - water enters from the bottom, flushes trapped debris up and out through the waste port, and you run it for 2-3 minutes until the sight glass or discharge water runs clear. A 30-second RINSE cycle reseats the sand, and the filter is clean. The entire process uses 200-500 gallons of water.

Who sand filters suit:

• Pool owners who want the simplest, fastest cleaning process
• Households with an existing backwash drain or acceptable drain area
• Owners of larger pools (20,000+ gallons) where cartridge cleaning becomes time-consuming
• Budget-conscious buyers - sand filters are the cheapest entry point

Honest downsides:

• 20-40 microns is the coarsest filtration of any residential filter - fine particles, some bacteria, and dead algae can pass through
• Each backwash cycle discharges 200-500 gallons - meaningful in drought-prone regions and where municipal water costs are high
• Sand channels over time (water finds paths of least resistance through the bed) - you may need to break up channeling with a backwash more often
• Can pass dead algae back into the pool during an algae bloom unless you add a flocking agent

Cost to own:

• Initial purchase: $200-600 for the filter (Hayward Pro Series S220T runs around $250-350; Pentair Triton II TR60 runs $300-400)
• Sand: $10-15 per 50 lb bag; a 24” filter typically needs 200-250 lbs ($40-75 of sand every 5-7 years)
• No other recurring media cost

Best for: Owners of large pools (25,000+ gallons) who want a 2-minute cleaning process and are not restricted from discharging backwash water.

Cartridge Filters - Best Filtration for Most Pool Owners

Cartridge filters use a pleated polyester element - the same basic concept as an automotive air filter - to strain particles down to 10-15 microns. Water flows from outside the pleated cylinder inward, and the fabric traps particles in and on the surface of the pleats.

How cleaning works: Unlike sand, cartridges cannot be backwashed. When pressure rises 8-10 PSI above your clean baseline, you shut off the pump, open the air relief valve, remove the cartridge, and rinse it with a garden hose - working top-to-bottom between every pleat. For a deeper monthly clean, soak the cartridge overnight in enzyme-based cartridge cleaner or a solution of 1 cup of trisodium phosphate per 5 gallons of water, then rinse thoroughly. The process takes 30-60 minutes.

Who cartridge filters suit:

• Most residential pools from 10,000 to 40,000 gallons
• Properties without a backwash drain or in water-scarce regions (cartridge cleaning uses roughly 10 gallons vs. 200-500 for backwashing)
• Owners willing to invest 30-60 minutes every 2-6 weeks in peak season
• Pools in areas with fine dust or pollen (finer filtration handles these better)

Honest downsides:

• Cleaning is more involved than backwashing - you cannot shortcut it
• During heavy algae blooms, cartridges can clog rapidly and require multiple cleanings per week
• Cartridge elements need replacement every 2-3 years regardless of cleaning diligence
• Multi-cartridge filters (like the Hayward SwimClear C4020 with 4 elements) mean cleaning 4 cartridges at once

Cost to own:

• Initial purchase: $300-800 (Hayward SwimClear C3020 at 300 sq ft runs $350-500; Pentair Clean & Clear Plus CC150 at 150 sq ft runs $250-400)
• Replacement cartridges: roughly $0.75 per sq ft - a 100 sq ft cartridge costs approximately $75, a 300 sq ft set costs approximately $225, every 2-3 years

Best for: Most residential pools 10,000-40,000 gallons, especially where backwash drainage is a constraint or water conservation matters.

DE Filters - Finest Filtration, Most Maintenance

Diatomaceous earth is the fossilized skeletal remains of microscopic aquatic organisms called diatoms. DE powder is white, chalky, and microscopic - when coated over a set of fabric-covered grids inside a filter tank, it creates a filtration surface capable of trapping particles as small as 3-5 microns. That is fine enough to catch most bacteria and nearly all algae cells.

How they work: After assembly, DE powder is loaded through the pool skimmer (it travels through the plumbing to coat the internal grids). Water flows through the DE-coated grids, gets filtered to 3-5 microns, and returns to the pool. When the grids load up, you backwash like a sand filter, then recharge with fresh DE powder through the skimmer.

Who DE filters suit:

• Owners who want the clearest possible water and will invest the time to maintain it
• Pools with high bather loads, heavy tree debris, or significant algae pressure
• Pools in bright-sun climates where water clarity shows clearly
• Commercial-adjacent residential pools (hotel pools, estate pools)

Honest downsides:

• Most complex maintenance of the three types - annual full teardown is non-negotiable
• DE powder is a nuisance dust (crystalline silica content - wear a dust mask when handling dry powder, per OSHA guidelines)
• If a grid tears, DE passes directly into the pool - white powder returning to the pool is a sign of grid failure
• Annual teardown means disassembling the tank, pulling out the grid manifold, cleaning every individual grid, inspecting for tears, soaking in DE cleaner, and reassembling - a 2-3 hour job

Cost to own:

• Initial purchase: $400-1,200 (Hayward Pro-Grid DE6020 runs $500-700; Pentair FNS Plus 60 runs $500-800)
• DE powder: roughly $1 per lb; charge is 1 lb per 5 sq ft of filter area, so a 60 sq ft filter needs 12 lbs at each recharge ($12 per backwash cycle, 4-8 cycles per season = $50-100/yr in DE powder)
• Annual grid inspection and possible grid replacement: individual grids run $15-30 each

Best for: Pools where water clarity is the top priority and the owner is prepared for annual teardown maintenance.

How to Size a Pool Filter

Undersizing a filter is one of the most common and costly mistakes. An undersized filter clogs faster, requires more frequent cleaning, creates higher back-pressure that strains the pump, and shortens both the filter and pump lifespan.

The sizing formula:

1. Determine your pool volume in gallons
2. Target 2 complete turnovers per day (your pump runs the pool volume through the filter twice)
3. Use the minimum sizing rule: 1 sq ft of filter area per 10,000 gallons; preferred is 1.5 sq ft per 10,000

For cartridge filters, sq ft is explicitly listed on the filter model (e.g., the Hayward SwimClear C4020 = 400 sq ft). For sand filters, the diameter is listed in the model number (S244T = 24” tank). For DE filters, sq ft is listed in the model name (Pentair FNS Plus 48 = 48 sq ft).

When in doubt, go one size up. The cost difference between a C3020 (300 sq ft) and a C4020 (400 sq ft) is roughly $100-150, but the C4020 will clean less frequently, run with lower back-pressure, and last longer.

Above-Ground vs. In-Ground Pools

Above-ground pools typically hold 5,000-15,000 gallons, run smaller pumps (3/4 HP to 1.5 HP range), and use 1.5” hose connections. Cartridge filters and small sand filters both work well. Most above-ground pool kits ship with a bundled filter - nearly always the minimum acceptable size. An upgrade to the next size up is almost always worthwhile.

Common above-ground filter sizes:

• 10,000 gal pool: Intex Krystal Clear 12” sand filter or 400 GPH cartridge; upgrade to Hayward S180T (18”) or 75 sq ft cartridge
• 15,000 gal pool: 18-22” sand filter or 75-100 sq ft cartridge recommended

In-ground pools hold 15,000-80,000+ gallons, run larger pumps (1 HP to 3 HP), and use 1.5” or 2” plumbing. All three filter types are viable. DE and cartridge both make sense for in-ground pools; sand is a practical choice for large pools where cartridge cleaning time becomes burdensome.

Pump matching matters. The filter must be sized to the pump’s flow rate. A 2 HP pump on a 50 sq ft cartridge will create destructive pressure. Check your filter’s maximum flow rate (GPM) and ensure the pump’s output at your head loss falls below that number.

Five Questions That Determine Your Filter

Answer these five questions honestly and the right filter type will be clear.

1. How much maintenance are you willing to do?

• Very little (15-minute max per cleaning session): sand filter
• Moderate (30-60 minutes every few weeks): cartridge filter
• Willing to invest 2-3 hours annually for a teardown: DE filter

2. Do you have an acceptable place to discharge backwash water?

• Yes (drain, landscaping, street with permission): sand or DE are viable
• No (no drain, drought rules, apartment complex): cartridge filter only

3. What is your pool volume?

• Under 15,000 gallons: cartridge or small sand
• 15,000-40,000 gallons: any type works; size accordingly
• Over 40,000 gallons: large sand filter or large DE system - cartridge cleaning at this volume becomes very time-consuming

4. Is water clarity your top priority?

• Yes: DE filter (3-5 microns is definitively superior)
• No: cartridge at 10-15 microns is excellent; sand is acceptable

5. What is your budget?

• Lowest initial cost: sand ($200-600)
• Middle range: cartridge ($300-800)
• Premium: DE ($400-1,200)

Note that initial cost is not the full picture. Factor in media replacement costs, water costs from backwashing, and your time.

What Pool Filter Competitors Don’t Tell You

Energy costs favor larger filters. A larger filter has lower resistance, which means your pump works less hard to push the same flow rate. Lower pump resistance = lower electricity consumption, especially with a variable-speed pump running at low RPM. An undersized filter that is partially clogged can add $10-30/month to your electricity bill compared to a properly sized one.

Oversizing is almost always better than exact-sizing. There is no penalty for a filter that is larger than the minimum. A bigger filter runs cleaner longer, cleans less frequently, and tolerates algae blooms without immediately clogging.

Variable-speed pump compatibility. All three filter types work with variable-speed pumps. DE and cartridge get more benefit because they filter finely even at low flow rates - you can run a DE or cartridge filter at 1,500 RPM overnight and still get excellent filtration. Sand filters at very low flow rates may not trap fine particles as effectively because the bed dynamics change.

The pump and filter must be matched. This is not optional. A pump that exceeds the filter’s maximum flow rate will damage the filter, blow out cartridges, and destroy DE grids. Before upgrading a pump, verify the new pump’s GPM output falls within the filter’s rated range.

Algae blooms punish cartridge filters. During an algae outbreak, a cartridge can clog in 24-48 hours. Sand filters handle algae blooms better because backwashing is fast and frequent. If your pool regularly deals with algae (heavy tree cover, southeast US climate, etc.), sand or DE may be more practical than cartridge.

Related Guides

• DE vs. Sand vs. Cartridge Filter - Full Comparison
• What Size Pool Filter Do I Need?
• How Long to Run Your Pool Filter
• Best Pool Filter Cleaner