Table of Contents
The Big Three Filter Types
Sand Filters
Sand filters are the workhorses of pool maintenance. They're affordable, durable, and require minimal maintenance beyond regular backwashing. Sand is the traditional filter media that creates a dense layer for trapping debris as water flows through.
How Sand Filters Work
- Water flows downward through sand bed (15-20 microns filtration)
- Debris accumulates on top layer
- Pressure builds over time (normal: 10-15 PSI)
- Backwash every 2-3 weeks or when pressure rises 7-10 PSI
- Media lasts 5-7 years before replacement
Best for: Large pools, high traffic areas, budget-conscious owners
Maintenance: Weekly backwashing, sand replacement every 5-7 years
Cartridge Filters
Cartridge filters use pleated polyester media that offers superior filtration without the need for harsh backwashing. They trap debris down to 10-15 microns and require less water waste during cleaning.
How Cartridge Filters Work
- Water flows through pleated polyester cartridge
- Fine filtration captures 10-15 micron particles
- Pressure builds as debris accumulates (normal: 15-20 PSI)
- Clean cartridge when pressure rises 7-10 PSI above baseline
- Cartridge lifespan: 3-5 years
Best for: Above-ground pools, low-flow systems, minimal backwash requirements
Maintenance: Rinse cartridge with garden hose, replace every 3-5 years
D.E. (Diatomaceous Earth) Filters
D.E. filters represent the pinnacle of pool filtration technology, capable of filtering particles down to 2-3 microns. They're the choice of serious pool operators who demand crystal clear water.
How D.E. Filters Work
- D.E. powder coats grid surfaces inside filter tank
- Finest filtration available: 2-3 microns
- Captures algae, bacteria, fine sediment
- Pressure builds rapidly due to fine filtration (normal: 15-25 PSI)
- Backwash and recharge D.E. every 2-3 weeks
- Replace grids every 5-7 years
Best for: Competitive pools, tournament facilities, maximum clarity requirements
Maintenance: Regular D.E. recharging, grid inspection, professional cleaning
Head-to-Head Comparisons
Choose the right filter type for your specific needs by comparing key factors:
| Feature | Sand | Cartridge | D.E. |
|---|---|---|---|
| Initial Cost | $300-600 | $400-800 | $500-1,200 |
| Filtration Rating | 15-20 microns | 10-15 microns | 2-3 microns |
| Backwashing Frequency | Every 2-3 weeks | Monthly | Every 2-3 weeks |
| Water Waste per Backwash | 200-500 gallons | 0 gallons | 200-500 gallons |
| Media Lifespan | 5-7 years | 3-5 years | 5-7 years (grids) |
| Operating Cost | $150-300/year | $100-200/year | $200-400/year |
| Maintenance Difficulty | Easy | Very Easy | Moderate |
| Best Pool Type | In-ground large | Above-ground small | High-traffic/tournament |
Alternative Filter Media
Beyond traditional sand, several advanced filter media options can dramatically improve water clarity and reduce maintenance:
Activated Filter Media (Glass)
Recycled glass media offers superior filtration compared to sand while being environmentally friendly. Glass media filters down to 3-5 microns, maintains lower pressure longer, and lasts 10+ years.
- Superior clarity and brightness
- Reduced backwashing frequency
- Won't cloud water like sand can
- Environmentally sustainable
- Compatible with existing sand filter tanks
Cellulose Fiber
A plant-based alternative that combines the efficiency of cartridge filters with the durability of sand. Cellulose fiber offers excellent value for medium-sized pools.
- Biodegradable and eco-friendly
- 10-15 micron filtration
- Lower pressure buildup
- Works in standard filter tanks
- Lasts 3-5 years
Interactive Filter Finder
Answer a few quick questions to find the perfect filter for your pool:
Pump & Filter Compatibility
The Golden Rule: 8-Hour Turnover
Your pump and filter must circulate your entire pool volume at least once every 8 hours. This is the foundation of proper pool chemistry.
Calculate your required GPM: Pool Volume ÷ 480 = Minimum GPM needed
Example: 15,000 gallon pool ÷ 480 = 31 GPM minimum pump size
Understanding Multiport Valves
The multiport valve is the command center of your filter system. It directs water flow in different directions to perform various maintenance functions:
The Six Multiport Valve Settings
- Filter: Normal operating mode. Water flows down through the filter media, trapping debris, and returns clean water to the pool. This is your default position for 95% of operation.
- Backwash: Reverses water flow to flush trapped debris out of the tank and down the waste line. Used when pressure rises 7-10 PSI above baseline. Typically run 2-3 minutes until water runs clear.
- Rinse: Returns water flow to normal direction but bypasses the filter media to rinse out loose particles. Run for 30-60 seconds after each backwash cycle. Essential for clarity.
- Waste: Bypasses the filter entirely and sends water straight to waste. Used to quickly drain the pool or remove heavy algae blooms without filtering. Also used for winter drainage.
- Recirculate: Circulates water without filtering. Useful for running chemical treatments through the system before filtering. Also used when skimmer is congested.
- Closed: Completely stops water flow. Never leave in this position during normal operation. Used only when servicing the filter or pump.
Seasonal Maintenance
The Clean Baseline Rule
Establish a pressure baseline for your filter when it's perfectly clean. Record this number at the start of each season. Your cleaning threshold is when pressure rises 7-10 PSI above this baseline—not an arbitrary "20 PSI" that other pools use.
Year-Round Maintenance Schedule
Spring (Pool Opening)
- Clean or replace filter media if stored wet over winter
- Inspect multiport valve for cracks or damage
- Check pump and filter housing for leaks
- Clean skimmer baskets and pump strainer
- Record clean filter pressure baseline
- Run backwash cycle to prime system
Summer (Heavy Use)
- Backwash every 2-3 weeks or when pressure rises
- Check pressure gauge daily
- Rinse cartridge every 30 days if cartridge filter
- Monitor for algae blooms requiring heavier filtration
- Inspect for cracks after heavy rain
Fall (Closing)
- Run final deep cleaning cycle
- Drain filter if winterizing in cold climates
- Clean and store cartridges in dry location
- Inspect grids for damage
- Clean multiport valve ports
Winter (Dormant)
- In mild climates, run filter 2-3 times per week at minimum
- Check for ice formation in pump and pipes
- Keep covers secure to prevent debris accumulation
- In cold climates, drain entire system and store indoors
Deep Cleaning Instructions
Backwashing Your Filter
Backwashing reverses water flow to flush trapped debris out of the filter media. It's the most important maintenance task you'll perform:
- Turn off the pump — Wait 30 seconds for pressure to stabilize
- Switch valve to Backwash — Gradually turn the multiport handle until it clicks
- Restart the pump — Water will flow out the waste line
- Watch the sight glass — Water should be dirty brown/gray initially
- Run until clear — Continue for 2-3 minutes until waste water is clear
- Turn off pump again — Let pressure drop to zero
- Switch to Rinse — Removes loose particles still in tank
- Run for 30-60 seconds — Until rinse water is clear
- Return to Filter — Back to normal operation mode
- Restart pump — System is now ready for operation
Deep Cleaning Cartridge Filters
Unlike sand filters, cartridge filters can't be backwashed. Instead, they're manually cleaned or chemically treated:
Manual Cartridge Cleaning
- Turn off pump and let pressure drop to zero
- Close the drain plug at bottom of filter housing
- Remove the filter housing lid (usually 4-6 bolts)
- Lift out cartridge carefully
- Rinse with garden hose from top to bottom (never sideways)
- Use soft brush for stubborn debris
- Soak in TSP (trisodium phosphate) solution for 4-8 hours for deep clean
- Rinse thoroughly and let air dry
- Reinstall cartridge and reassemble housing
- Open drain plug and restart pump
Troubleshooting Matrix
Use these diagnostic cards to identify and fix common filter problems:
Low Pressure (Below Normal)
Possible Causes:
- Pump not running or underpowered
- Air leaks in system (wet pump area)
- Skimmer basket clogged
- Pump strainer basket full of debris
- Multiport valve set to recirculate
- Cartridge torn and needs replacement
Solutions: Check pump operation, inspect all connections for cracks, clean skimmer and pump baskets, reset valve to filter, replace cartridge if damaged.
High Pressure (7-10 PSI Above Baseline)
Possible Causes:
- Filter media clogged with debris (normal condition)
- Multiport valve partly closed
- Return line kinked or clogged
- Pressure gauge faulty
- Filter housing cracked internally
Solutions: Backwash immediately, check valve position, inspect plumbing lines, replace gauge if reading inconsistently, inspect for leaks indicating internal damage.
Sand in Pool (Cloudy Water After Backwash)
Possible Causes:
- Cracked or bridged filter media bed
- Multiport valve not fully switched to rinse
- Sand media settling too much in tank
- Return line filter sock clogged
- Damaged lateral beneath sand bed
Solutions: Run longer rinse cycle, ensure valve clicks fully into rinse position, check lateral assembly for cracks, replace filter sock, may need professional internal inspection.
Pro Filter Hacks
These insider tricks will save you time and money while improving filter performance:
Skimmer Sock Trick
Add a mesh skimmer sock to your main skimmer basket. This pre-filter catches fine debris before it reaches the pump strainer and main filter, reducing cleaning frequency by up to 50%. Replace weekly or when visibly clogged. This is a game-changer for high-wind areas or wooded properties.
Shop Skimmer SocksTennis Ball Oil Trap
Throw 3-4 clean tennis balls into your pool during the season. The fuzz on the balls naturally absorbs sunscreen, body oils, and lotions that would otherwise coat your cartridge and reduce efficiency. Replace the tennis balls every 2 weeks. This prevents "oily" cartridge syndrome that no amount of cleaning solves and extends cartridge life by 6-12 months.
Shop Tennis BallsTest Your Filter Mastery
When should you backwash your sand filter?
Related Tools
Need Help With Your Equipment?
Whether you need a filter tear-down, a sand change, or you are fighting a cloudy pool that just won't clear, we have you covered.
Frequently Asked Questions
How often should I clean my pool filter?
Most filters need cleaning when the pressure gauge reads 7-10 PSI above the baseline (when the filter was perfectly clean). For sand filters, that's typically every 2-3 weeks during regular use. For cartridge filters, that's typically every 3-6 months. For D.E. filters, that's typically every 2-3 weeks. The key is to establish your own baseline pressure, not go by what other pool owners tell you.
What's the difference between sand, cartridge, and D.E. filters?
Sand filters are the most affordable and durable, using sand as the filter media. They filter down to 15-20 microns and last 5-7 years. Cartridge filters are more efficient and require less backwashing, filtering to 10-15 microns. D.E. filters offer the finest filtration available at 2-3 microns but require more maintenance. Choose based on your pool size, budget, and desired water clarity.
Can I clean and reuse my D.E. filter?
Yes, D.E. filter grids can be cleaned and reused multiple times. Backwash the filter, then use a garden hose to gently clean the grids. For a deep clean, soak the grids in a mild TSP solution for 4-8 hours. After 5-7 years of use, the grids may become brittle and need replacement. Replace grids in sets to ensure even filtration performance.
What GPM pump do I need for my pool?
The golden rule is to turn over your entire pool volume every 8 hours. Divide your pool volume by 480 (8 hours × 60 minutes) to get the required GPM. A typical 15,000-gallon pool needs about 31 GPM. A 25,000-gallon pool needs about 52 GPM. Always select a pump sized at least to your minimum calculated GPM for proper water circulation and chemical distribution.
Not Sure Which Filter You Have?
A Pool Pro Can Inspect and Diagnose It in Minutes.
Filter problems often look similar but have very different fixes. A local professional can identify your filter type, check for internal damage, and recommend whether a cleaning, media replacement, or full upgrade makes more sense.
Related: How to Add DE to a Sand Filter · Equipment Troubleshooter