Sand vs cartridge vs glass media vs DE: choosing a pool filter for a Sunshine Coast pool

Neither a sand filter nor a cartridge filter is better for every pool: sand (or glass media) suits owners who want to backwash and walk away, while a cartridge suits owners who would rather hose a cartridge than send hundreds of litres of backwash to the sewer. Glass media and DE sit either side, trading cost and handling for finer filtration.

Sand vs cartridge pool filter: the short answer

A sand filter is the simpler, lower-effort choice, and a cartridge filter is the water-saving, finer-filtering choice, but each maker rates fineness differently. Zodiac says its CS cartridge catches particles of 10 to 20 microns against 25 to 40 microns for sand, while Waterco rates cartridges at about 30 microns and sand or media at 3 to 40 microns depending on the media. The practical difference on a Sunshine Coast pool is the cleaning routine: a sand filter is cleaned by backwashing to a lawful waste outlet (on sewered properties, the sewer), and a cartridge is lifted out and hosed.

Side-by-side: sand, glass media, cartridge and DE filters compared

The four common filter types differ mainly in how fine they filter, how they are cleaned and what you replace over time; none wins on every factor. Glass media and zeolite products go into the same tank as sand, so a media filter can change character without changing the tank. Zodiac says its Titan media filters accept silica sand, coarse and fine glass media, and Diamond Brite. Diamond Brite is not glass: Zodiac lists it with zeolite in its media weights and calls it an alternative filter media to sand that filters particles down to 3 microns.

Sand and glass media filters: how they work, strengths and downsides

A sand or glass media filter pushes water through a deep bed of media that traps dirt, and it is cleaned by reversing the flow. In Zodiac’s sand filter manual, the BACKWASH position sends water up through the bed and out the waste line, followed by a short RINSE before returning to FILTER. Waterco lists durability and easy cleaning without taking the filter apart as the main strengths. The downsides Waterco lists are regular backwashing that can use a lot of water, a larger installation space and media replacement about every five years.

Glass media is one alternative to sand in the same tank. Zodiac describes its Crystals as a direct replacement for sand or zeolite, sold in coarse and fine grades, and says glass is far less prone to clogging than sand. Waterco rates its Glass Pearls at 3 microns. Waterco also sells ZeoPlus, a zeolite media it says lowers chlorine demand by removing ammonia, but it notes the media needs regeneration to keep working. Waterco notes that glass and ZeoPlus both cost more than sand, so the trade is a higher media spend for better clarity, and with glass, less backwash water.

Cartridge filters: how they work, strengths and downsides

A cartridge filter traps dirt on pleated fabric elements, and it is cleaned by taking the cartridge out and hosing it rather than by backwashing. Zodiac’s instruction for its CS range is simply to remove the cartridge element and hose it down. Waterco lists the strengths as no backwashing, no backwash line and a smaller footprint, which matters on tight equipment pads and on pools without a sewer connection for waste. The downsides Waterco lists are that the filter must be opened and cleaned by hand, and that cartridges may need replacing more often than sand or glass media.

Switch the pump off before opening any filter lid, and follow your model’s manual. On a leafy block, keep the skimmer and pump baskets emptied: whatever the baskets catch never reaches the cartridge. If you are weighing up a robotic cleaner as well, see our Dolphin robotic pool cleaners.

What is a DE filter, and is it worth it for a home pool?

A DE filter uses a fine powder called diatomaceous earth, made from fossilised algae, which coats grids inside the tank and forms the filter cake that strains the water. Waterco describes it as trapping anything larger than 2 microns on one page and 3 to 5 microns on another, which places DE at the fine end of every comparison.

DE is worth it for owners who want the finest polish and will handle the powder each time. Waterco notes that DE needs backwashing, though less often than sand, and that the DE has to be replaced each time you backwash. That powder is also the handling concern. One Australian safety data sheet (SDS) for a flux-calcined diatomaceous earth product lists crystalline silica as an ingredient and warns not to breathe the dust, and Safe Work Australia says breathing in respirable crystalline silica can cause serious irreversible lung diseases like silicosis and lung cancer. If you choose DE, read the SDS for the exact powder you buy and follow its handling and protective equipment advice. If you would rather not handle it at all, have a technician service the filter.

Which filter suits your pool? A decision table for Sunshine Coast conditions (trees, storms, salt pools, rentals)

The right filter depends on the pool’s situation more than on the filter itself, so match the filter to who cleans it, how much debris it gets and where waste water can go. The table below compares the trade-offs for common Sunshine Coast setups, from Noosa hinterland blocks under trees to coastal holiday lets. It is a guide to the trade-offs, not a ranking.

For salt pools, the sanitiser choice is covered in our guide to salt vs chlorine pools.

Backwash water, water use and where it can go in Queensland

In Queensland, backwash water must not go into the stormwater system or a roadside gutter. The Environmental Protection Regulation 2019 lists “waste water, including backwash from swimming pools” as a prescribed water contaminant. Section 440ZG of the Environmental Protection Act 1994 makes it an offence to unlawfully deposit one in waters, a roadside gutter or stormwater drainage. That includes leaving it where it could reasonably be expected to wash into them, so backwashing onto a sloping lawn that drains to the street is a risk.

On a sewered property, Unitywater’s policy sets out how backwash can go to sewer. Unitywater’s Domestic Swimming Pool Wastewater Disposal Policy says backwash water may be contaminated with pathogens or harmful substances. It accepts backwash from domestic pools to its sewer at up to 0.5 litres per second, and a licensed plumber and drainer can connect a backwash line to private sanitary drains. Water drawn down for maintenance is treated differently: Unitywater prefers it reused, for example on lawns or gardens. If it goes to sewer, it goes through the overflow relief gully between 10am and 5pm or 10pm and 5am, at no more than 0.5 litres per second through an air gap, and only if reuse is not safe or practical. Zodiac puts an average sand backwash at 750 litres, which is the volume a cartridge or glass media avoids or reduces; the actual volume depends on pump flow and how long you backwash.

How long each filter type lasts and signs it is due for new media or cartridges

Sand media lasts about five years according to Waterco, glass media is claimed to degrade more slowly, cartridges are replaced as use and care demand, and DE powder is replaced at every backwash. Waterco gives no year figure for glass, so treat longer-life claims as relative to sand rather than a fixed number. Waterco says how often cartridges need replacing depends on the level of use and care. For water chemistry targets, see our chlorine and pH guide.

The pressure gauge is the main signal. Zodiac’s manual tells owners to note the gauge reading when the filter is clean, because pressure rises and flow drops as dirt builds up. Owner observations worth having a technician check include:

• pressure that climbs back soon after a backwash or cartridge clean;
• cloudy water that persists despite correct chemistry and run time;
• cartridge pleats that look torn or flattened;
• media or grit appearing in the pool.

Persistent low flow can also come from the pump; our pool pump troubleshooting guide covers those checks. A filter or valve that drips water can be part of a wider loss, which our guide on how to tell if a pool is leaking walks through.

Sizing a replacement filter to your pump: what you can check vs when to call a technician

Manufacturers publish a maximum flow in litres per minute for each model; compare it with your pump’s flow and ask a technician to confirm the match. Zodiac lists 185 L/min for its 21 inch Titan ZT500 media filter and 379 L/min for its CS100 cartridge filter. A bigger media tank needs more media (Zodiac’s ZT500 alone takes 85 kg of sand) and more space. If you are also changing pumps, our variable speed pool pump guide explains how pump speed affects flow.

Zodiac’s manual warns that a filter operates under high pressure and that trapped air can blow a lid or valve off, so leave anything beyond basket, backwash and cartridge cleaning to a professional. For a filter swap, media change or a second opinion on sizing, book pool repairs on the Sunshine Coast or ongoing pool maintenance with Billabong Pool Service, or visit the shops in Noosa, Maroochydore and Caloundra.