Choosing the correct pool filter ensures clear water, proper flow, and longer equipment life. An undersized filter will clog quickly and reduce circulation, while an oversized filter improves filtration and reduces maintenance.
Filter Types Explained
Cartridge Filters
- No backwashing required
- Excellent filtration (10-20 microns)
- Lower water usage
- Cleaned manually
Best for: Most residential pools, water-conscious owners
Sand Filters
- Easy to operate
- Backwash to clean
- Lower filtration (20-40 microns)
Best for: Simplicity, minimal hands-on maintenance
DE (Diatomaceous Earth) Filters
- Finest filtration (2-5 microns)
- Backwashing + DE recharge required
- Highest water clarity
Best for: Maximum water clarity, experienced pool owners
Filter Size by Pool Volume
Rule of thumb: Bigger is always better with filters.
Cartridge Filters (Total Square Footage)
| Pool Size (Gallons) | Cartridge Filter Size |
|---|---|
| Up to 15,000 | 100 – 150 sq. ft. |
| 15,000 – 25,000 | 150 – 300 sq. ft. |
| 25,000 – 35,000 | 300 – 500 sq. ft. |
| 35,000+ | 500+ sq. ft. |
✔ Larger cartridges = longer time between cleanings
Sand Filters
| Pool Size (Gallons) | Sand Filter Size |
|---|---|
| Up to 15,000 | 200 lb |
| 15,000 – 25,000 | 300 lb |
| 25,000 – 35,000 | 350 lb |
| 35,000+ | 500+ lb |
DE Filters
| Pool Size (Gallons) | DE Filter Size |
|---|---|
| Up to 15,000 | 24 sq. ft. |
| 15,000 – 25,000 | 36 sq. ft. |
| 25,000 – 35,000 | 48 sq. ft. |
| 35,000+ | 60 – 72 sq. ft. |
Match the Filter to Your Pump
Your filter must handle the maximum flow rate (GPM) of your pump.
| Plumbing Size | Typical Max Flow |
|---|---|
| 1 1/2″ PVC | ~45 GPM |
| 2″ PVC | ~65 GPM |
| 2 1/2″ PVC | 80+ GPM |
⚠️ Running a pump that exceeds the filter’s flow rating can:
- Damage internal components
- Reduce filtration efficiency
- Void manufacturer warranties
Why Oversizing a Filter Is Good
✔ Cleaner water
✔ Lower pressure
✔ Longer time between cleanings/backwashing
✔ Longer filter life
✔ Better compatibility with variable-speed pumps
A larger filter paired with a lower pump speed is the most efficient setup.
Special System Considerations
You may need a larger filter if your pool has:
- Variable-speed pump running long hours
- In-floor cleaning system
- Heavy debris (trees, leaves)
- Spa spillover
- High swimmer load
Common Filter Sizing Mistakes
❌ Matching filter size to pump HP only
❌ Choosing the minimum recommended size
❌ Ignoring maximum flow rating
❌ Underestimating debris load
✅ Always size for flow rate and pool volume
Replacing an Existing Filter?
Check the filter label for:
- Filter type
- Square footage (cartridge / DE)
- Tank diameter (sand)
- Maximum flow rate (GPM)
If you’re unsure, contact us and we’ll help you choose the correct filter.
