Choosing a Pool Filter: Why It Matters
Your pool filter is responsible for removing contaminants — from visible debris to microscopic particles — from your water. It works hand-in-hand with your sanitizer (chlorine or otherwise) to keep your pool safe and clear. Choosing the wrong filter for your situation can mean more maintenance, higher costs, or water that never quite looks right.
There are three main filter technologies: sand, cartridge, and diatomaceous earth (DE). Here's how to choose between them.
How Each Filter Type Works
Sand Filters
Sand filters pass pool water through a tank filled with specially graded filter sand (or alternative media like glass or zeolite). Particles down to approximately 20–40 microns are trapped in the sand bed. When the sand becomes clogged, you "backwash" — reversing the water flow to flush contaminants to waste.
Cartridge Filters
Cartridge filters use pleated polyester filter elements (similar to an air filter) to capture particles down to approximately 10–15 microns. Maintenance involves removing the cartridge and rinsing it with a garden hose. Cartridges need periodic deep cleaning and eventual replacement.
Diatomaceous Earth (DE) Filters
DE filters use a powder made from fossilized diatom shells to coat internal grids. This medium can filter particles down to approximately 3–5 microns — making them the most powerful filtration option available. DE requires periodic backwashing and "recharging" with fresh DE powder.
Side-by-Side Comparison
| Feature | Sand | Cartridge | DE |
|---|---|---|---|
| Filtration (microns) | 20–40 | 10–15 | 3–5 |
| Upfront Cost | Low | Medium | Higher |
| Maintenance Frequency | Backwash as needed | Rinse every 1–2 months | Backwash + recharge periodically |
| Water Usage | High (backwash) | Low (no backwash) | Medium (backwash) |
| Water Clarity | Good | Very Good | Excellent |
| Media Replacement | Every 5–7 years | Every 3–5 years (cartridge) | DE powder (annually) |
Sand Filters: Best For...
- Pool owners who want the lowest maintenance burden — backwashing takes minutes
- Larger pools where cartridge size would be impractical
- Areas with high debris loads (lots of trees, leaves)
- Those on a tight initial budget
Consider upgrading the media: Replacing standard filter sand with filter glass or zeolite can improve filtration to around 5–10 microns without changing your filter tank.
Cartridge Filters: Best For...
- Pool owners in areas with water restrictions — no backwashing means significant water savings
- Above ground and smaller inground pools
- Those who prefer straightforward, no-valve maintenance
- Situations where very good (not just adequate) water clarity is the goal
DE Filters: Best For...
- Pool owners who prioritize crystal-clear water above all else
- Pools that host frequent parties or heavy swimmer loads
- Those comfortable with slightly more involved maintenance routines
- Larger inground pools where the investment is justified by performance
Sizing Your Filter
Filter sizing matters as much as type selection. An undersized filter will clog quickly and strain your pump. As a general guideline, choose a filter rated for a pool size larger than yours — this gives you a buffer and extends cleaning intervals. Always match the filter's flow rate (in GPM) to your pump's output.
The Bottom Line
For most homeowners, a cartridge filter hits the sweet spot of filtration quality, water conservation, and easy maintenance. If you want the absolute clearest water and don't mind extra upkeep, go with DE. If budget is your primary concern and you have a larger pool, a quality sand filter with upgraded media is a solid choice.
Whatever you choose, a properly sized, well-maintained filter is the cornerstone of a clean, healthy pool.