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Pool filtration boils down to three technologies: cartridge, sand, and diatomaceous earth (DE). Each has strengths, weaknesses, and a specific personality. If you're building a pool, replacing a failed system, or choosing between options, here's the honest breakdown.
The three pool filter types
Despite marketing complexity, pool filters only filter water in three ways:
- Cartridge: pleated fabric traps debris like a coffee filter
- Sand: water passes through a bed of specialized sand, debris catches in gaps
- DE: water passes through a fossilized algae coating on grids, catching extremely fine particles
Cartridge filters
How it works: Water enters the filter tank, passes through pleated polyester cartridges, and returns to the pool. Debris collects on the cartridge surface.
Filtration: 10-20 microns. Very good water clarity.
Maintenance: Remove cartridges every 4-6 weeks, hose them down, reinstall. Replace every 2-3 years.
Cost: Mid-range upfront. Replacement cartridges $30-$100 each depending on size.
Strengths: No backwashing (water savings). Good filtration. Reasonable maintenance.
Weaknesses: Physical cleaning required. Heavier debris loads lead to more frequent cleaning. Replacement cost adds up.
Best for: most modern pools, especially where water conservation matters.
Sand filters
How it works: Water flows into a pressurized tank containing filter sand. Debris catches in gaps between sand grains. When pressure rises, you backwash — reversing flow to flush accumulated debris out the waste line.
Filtration: 20-40 microns. Good but leaves slight haze on sensitive eyes.
Maintenance: Backwash every 1-4 weeks based on pressure. Replace sand every 5-7 years.
Cost: Lowest upfront and ongoing. Sand costs $20-$40 per replacement.
Strengths: Lowest total cost of ownership. Simple operation. Very durable.
Weaknesses: Uses water during backwash (100-300 gallons each time). Coarser filtration. Not legal in some water-restricted areas.
Best for: budget-conscious, larger pools, areas with plentiful water.
DE (Diatomaceous Earth) filters
How it works: DE powder (microscopic fossilized algae skeletons) coats a grid or fingers inside the filter. Water passes through the DE coating, which traps extremely fine particles.
Filtration: 2-5 microns. Exceptional water clarity — often described as "crystal clear" or "champagne clear."
Maintenance: Backwash as needed (pressure-based). Add fresh DE powder after each backwash. Break down and deep-clean annually.
Cost: Highest upfront. DE powder $20 per bag, lasts a few months.
Strengths: Best filtration available. Removes particles other filters can't touch. Great for shared/hotel pools.
Weaknesses: Most maintenance. DE powder is messy. Water usage on backwash. Old DE must be disposed of carefully. Not legal everywhere.
Best for: pool owners prioritizing water quality above all else.
Used DE powder contains concentrated pool debris and should not be dumped on lawns or into storm drains. Many jurisdictions regulate DE disposal. Check local rules before installing.
Which type suits your climate
- Desert Southwest (water-restricted): Cartridge. Sand and DE backwash waste too much water.
- Humid South (heavy pollen, algae pressure): DE for small pools; cartridge for mid-size; sand for large.
- Northern regions (short pool season): Sand is fine. The coarser filtration matters less when you only use the pool 3-4 months.
- Coastal areas: Cartridge. Sand corrodes faster in salt-air environments.
Side-by-side comparison
| Cartridge | Sand | DE | |
|---|---|---|---|
| Filtration | 10-20µm | 20-40µm | 2-5µm |
| Upfront cost | $400-$800 | $300-$600 | $500-$1,000 |
| Maintenance | Medium | Low | High |
| Water usage | Minimal | High (backwash) | High (backwash) |
| Replacement cost | $30-100 every 2-3 yr | $30 every 5-7 yr | $20 DE per refill |
| Water clarity | Very good | Good | Exceptional |
Frequently asked questions
Can I convert one type to another?
Usually yes — the tank/housing can sometimes be converted with a different media setup, or you can replace the entire filter unit. Costs $400-$1,500 depending on complexity.
Which is best for saltwater pools?
Cartridge. Sand systems can corrode valves; DE adds another thing to maintain. Cartridge is simplest with salt.
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