What a Pool Filter Does

A pool filter removes suspended particles from the water — everything from dead skin cells and sunscreen residue to fine dust, pollen and dead algae. It does this by passing water through a filtration medium (sand, glass or a cartridge membrane) that traps particles above a certain size.

The filter does not sanitise the water — that's chlorine's job. What it does is remove the physical matter that would otherwise make the water cloudy, consume chlorine, and provide surfaces for bacteria and algae to colonise.

Filter performance depends on three things: the filtration medium's ability to trap particles, the flow rate through the filter, and how long the pump runs each day. A perfect filter running two hours achieves far less than an adequate filter running twelve.

Media Filters

Media filters are the most common filter type in Australia. Water passes down through a bed of filtration media and debris is trapped in the spaces between the particles. When the filter is dirty, it is backwashed — water is reversed through the media bed, flushing trapped debris to waste.

The two media options are sand and glass. Sand (typically 20mm sharp silica sand) filters particles down to around 20–40 microns and is the traditional choice — durable, low cost, and easy to maintain. Glass media uses recycled glass particles in the same tank design but filters to approximately 5–10 microns, producing noticeably clearer water. The irregular shape and electrostatic properties of glass also reduce channelling and require less water per backwash cycle. Glass media lasts longer (7–10 years versus 5–7 years for sand) but costs more upfront. In most cases, a sand filter can be upgraded to glass media simply by swapping the media — worth considering whenever your sand is due for replacement.

Pros:

• Durable and suitable for pools with high debris loads

• Easy to maintain with regular backwashing

• Glass media option delivers superior filtration and longer media life

Cons:

• Sand can channel over time, reducing filtration efficiency

• Regular backwashing uses water (less so with glass media)

• Higher upfront cost if choosing glass media

Channelling is the most common media filter failure. If your pool is persistently cloudy despite correct chemistry and adequate pump run time, channelling may be the cause. Test by turning off the pump, waiting 10 minutes, then restarting — if pressure drops immediately to normal, channelling was likely the issue. Backwash thoroughly and consider a media refresh.

Cartridge Filters

Cartridge filters use a pleated polyester element to filter water. Unlike sand and glass, there is no backwashing — when the cartridge is dirty, it's removed and cleaned with a hose.

Pros:

• No backwash water waste — good for water-conscious households

• Filters to approximately 10–15 microns

• Lower pressure operation — works well with variable speed pumps at low speed settings

• Simpler plumbing — no backwash valve required

Cons:

• Cartridges need regular removal and hosing (every 6–8 weeks)

• Cartridges need replacing periodically (typically every 1–2 years)

• Not suitable for pools with heavy debris load — cartridge clogs quickly

• Cannot be used during green pool recovery without very frequent cartridge removal

Cartridge filter maintenance: remove and hose clean every 6–8 weeks during regular use. Soak in cartridge cleaner solution twice per year to remove oils and mineral scale that hosing doesn't clear. Replace when the element shows fraying, cracking or permanent discolouration.

Which Filter Is Right for Your Pool?

High debris load (trees nearby, large pool):

Sand or glass media with backwash capability. The ability to backwash makes managing high debris loads practical.

Water conservation is a priority:

Cartridge filters have a significant advantage here — no backwash water loss. Glass media also uses less water per backwash cycle than sand.

Crystal-clear water is the goal:

Glass media offers the best filtration in a backwash filter. Cartridge also filters well for the right pool.

Paired with a variable speed pump:

Cartridge filters run at lower pressure, which pairs well with VSPs at low speed. Sand and glass filters generally require slightly higher flow rates to function correctly.

Filter Maintenance: What You Need to Do

Media filters:

• Backwash when pressure rises 50–70 kPa above clean operating pressure, or at least every four weeks

• Check pressure gauge regularly — a drop in pressure with reduced return flow can indicate a failed laterals assembly

• Replace sand media every 5–7 years, glass media every 7–10 years

Cartridge filters:

• Remove and hose clean every 6–8 weeks

• Deep clean with cartridge cleaner every 3–6 months

• Replace cartridge every 1–2 years or when damaged

For all filter types: check the filter lid and drain o-ring annually. A deteriorating o-ring causes air ingestion, reduces pump efficiency, and will eventually cause a complete seal failure.

When to Replace Your Filter Media or the Whole Filter

Signs filter media needs replacement:

• Pool persistently cloudy despite correct chemistry and adequate pump run time

• Backwashing more frequently than usual — media has broken down

• Media is more than 7 years old (sand) or 10 years old (glass)

Signs you may need a new filter tank:

• Tank is visibly bowed or cracked

• Persistent leaking around fittings that can't be resolved with o-ring replacement

• Filter is undersized for the pool — common in older installations where minimum rather than optimal sizing was used

At Atlantis Pool Services, we supply and install all three filter types across North Lakes, Mango Hill, Kallangur, Redcliffe and the wider North Brisbane region. If you're unsure whether your filter is appropriate or performing as it should, call us on (07) 3491 9700 for an assessment.