Pool Filter Systems Explained
How sand, cartridge, and DE filters work, what they cost, and how to match the filter to your pool and maintenance expectations.
What the filter does
The filter's job is to remove particles from the water — dirt, debris, algae, and fine material that the pump circulates through the system. A well-matched filter keeps the water clear, reduces chemical demand, and protects the plumbing and heat exchange surfaces.
There are three main filter types used in Australian residential pools: sand, cartridge, and diatomaceous earth (DE). Each has different performance characteristics, maintenance requirements, and costs.
The filter is part of a system — pump, filter, chlorinator, and plumbing all need to be matched. Ask about the whole setup, not just the filter.
Use this guide to narrow the conversation.
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Clarify the constraint
Work out whether the main issue is space, access, budget, approvals, finish, or long-term maintenance.
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Keep a short brief
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Sand filters
How they work
Water passes through a bed of specially graded sand (typically silica sand or glass media). Particles are trapped in the spaces between the sand grains. When the filter becomes dirty, it is backwashed — water flow is reversed to flush accumulated debris to waste.
Advantages
- Low maintenance — backwashing is straightforward and does not require opening the filter
- Durable media — sand or glass media lasts 3–5 years before replacement
- Tolerant — handles periods of neglect better than other types
- Lower upfront cost — generally the most affordable filter option
Disadvantages
- Coarser filtration — captures particles down to approximately 20–40 microns (cartridge and DE filter finer)
- Water waste — backwashing sends water to waste, which can be significant over a season
- Media replacement — sand compacts over time and needs periodic replacement
Glass media upgrade
Replacing silica sand with glass filter media improves filtration fineness (down to approximately 10–15 microns) and resists algae growth within the filter bed. A worthwhile upgrade for most sand filter installations.
Cartridge filters
How they work
Water passes through a pleated cartridge made of polyester or similar material. Particles are trapped on the surface and within the pleats. When the cartridge becomes dirty, it is removed and cleaned (hosed off) or replaced.
Advantages
- Fine filtration — captures particles down to approximately 10–20 microns, producing very clear water
- No water waste — cleaning does not require backwashing
- Quiet operation — typically runs at lower pressure than sand filters
- Good for smaller pools — compact units available for plunge pools and smaller systems
Disadvantages
- More hands-on maintenance — cartridges must be removed and cleaned every 4–8 weeks (more often with heavy use)
- Cartridge replacement cost — cartridges last 1–2 years and are not inexpensive
- Less forgiving — if the pool is neglected, the cartridge can clog quickly and restrict flow
DE (diatomaceous earth) filters
How they work
DE is a fine powder made from fossilised organisms. It coats a set of internal grids or fingers, forming an extremely fine filtration layer. Water passes through the DE coating, which traps particles as small as 2–5 microns — the finest of all three filter types.
Advantages
- Finest filtration — produces the clearest water of any filter type
- Excellent for pools with fine debris — effective against algae spores and very fine particles
- Good flow rates — typically handles high flow without excessive pressure
Disadvantages
- Most complex maintenance — requires DE powder to be added after each backwash, and grids must be periodically soaked and inspected
- DE powder handling — DE is a fine dust that should not be inhaled. Care is needed during handling.
- Higher cost — both upfront and ongoing (DE powder, grid replacement)
- More components — more parts that can fail or need attention
Comparison at a glance
| Factor | Sand | Cartridge | DE |
|---|---|---|---|
| Filtration fineness | 20–40 microns | 10–20 microns | 2–5 microns |
| Backwash required | Yes (water to waste) | No (remove and clean) | Yes (water to waste) |
| Maintenance frequency | Low | Medium | High |
| Upfront cost | Lowest | Medium | Highest |
| Ongoing cost | Low | Medium | Medium–high |
| Water waste | Moderate | None | Moderate |
| Best for | Low-maintenance preference | Smaller pools, clear water priority | Highest water clarity |
Matching the filter to the pool
- Small pools and plunge pools — a cartridge filter is often the best fit. Compact, effective, no backwash waste.
- Family pools with heavy use — sand with glass media or cartridge, depending on maintenance tolerance.
- Pools with surrounding trees or debris — sand handles heavy debris loads well; cartridge may clog quickly.
- Pools where water clarity is paramount — DE provides the finest filtration.
The filter is part of a system
The filter does not work alone. The pump, chlorinator, and plumbing all need to be matched:
- Pump sizing — the pump must be matched to the filter's flow rate. An oversized pump can damage the filter; an undersized pump reduces filtration.
- Run time — most pools need 6–8 hours of pump run time daily (more in summer). Variable-speed pumps can reduce energy costs significantly.
- Chlorinator type — salt systems, liquid dosing, or tablet feeders all interact differently with the filtration cycle.
- Plumbing — pipe diameter, fittings, and valve design affect pressure and flow.
Maintenance schedule
| Task | Sand | Cartridge | DE |
|---|---|---|---|
| Routine clean | Backwash every 4–6 weeks | Hose off cartridge every 4–8 weeks | Backwash every 4–6 weeks |
| Deep clean | Replace media every 3–5 years | Replace cartridge every 1–2 years | Soak grids annually; replace every 3–5 years |
| Check | Pressure gauge, multiport valve | Pressure gauge, O-rings | Pressure gauge, grid condition, DE supply |
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