Pool Filters Explained – Part 3

Part 3: Pool Filter Media Explained – Sand, Glass and Zeolite

Although the filter housing is often the most visible part of a filtration system, the real work is performed by the material inside it. Known as the filter media, this material traps suspended particles as water passes through the filter.

Choosing the right media can influence water clarity, maintenance requirements, water consumption and the long-term operating costs of your pool.

Today, most Australian swimming pools use one of three filter media:

• Silica sand
• Recycled glass media
• Zeolite

Each has its own strengths and limitations, and understanding these differences will help you make an informed decision when it’s time to replace your filter media.

What Does Filter Media Actually Do?

A common misconception is that filter media acts like a kitchen sieve, where particles larger than the holes are trapped and smaller particles simply pass through.

In reality, filtration is much more complex.

As water moves through the filter bed, particles are removed by several different mechanisms, including:

• Mechanical straining
• Interception
• Sedimentation
• Adsorption onto the media surface
• Random particle collisions within the filter bed

Because these processes work together, filters can often capture particles much smaller than the spaces between the media grains.\

The Science Behind It

The particles suspended in pool water vary enormously in size.

Approximate sizes include:

Most pool filters are designed to remove suspended particles not individual bacteria. That’s why filtration must always work together with effective sanitation.

Silica Sand

Silica sand has been the industry standard for decades and remains the most widely used filter media in Australia.

It is not ordinary beach or construction sand.

Pool filter sand is a carefully graded, high-purity silica material manufactured to precise particle sizes. This consistency allows water to flow evenly through the filter while effectively trapping suspended debris.

Provided it is installed correctly and maintained properly, silica sand provides reliable performance for many years.

Advantages of Silica Sand

Silica sand continues to be popular for several reasons.

It is:

• Proven technology with decades of successful use.
• Readily available.
• Cost-effective.
• Easy to install.
• Compatible with almost every media filter.
• Well understood by pool technicians.

Many residential pools continue to operate perfectly with silica sand after years of reliable service.

Limitations

Over time, repeated backwashing, water chemistry and mechanical wear gradually alter the surface of the sand grains.

As the particles become smoother, filtration efficiency can slowly decline.

Organic matter, calcium deposits and oils may also accumulate within the media bed if water chemistry is poorly maintained.

Eventually the media should be replaced.

For most residential pools this occurs approximately every 5 to 8 years, although some pools may require earlier replacement depending on operating conditions.

Technician’s Tip
Replacing the filter media is often overlooked because the pool may still appear reasonably clear. However, older media can contribute to longer recovery times after storms, increased backwashing and reduced overall filtration efficiency.

Glass Media

Glass media has become increasingly popular as an alternative to silica sand.

It is typically manufactured from recycled glass that is crushed, cleaned, polished and graded into carefully controlled particle sizes suitable for filtration.

Unlike broken household glass, quality pool filter glass has smooth edges and is specifically engineered for use inside pressure filters.

Many manufacturers claim glass media provides improved filtration while reducing water consumption and extending the interval between backwashing.

There is certainly evidence that glass media performs very well in many installations, although the degree of improvement depends on the overall filtration system rather than the media alone.

Potential Benefits

Many pool owners choose glass media because it may provide:

• Improved capture of fine suspended particles.
• Reduced backwashing frequency.
• Lower long-term water consumption.
• Longer service life.
• Good resistance to media compaction.
• A productive use for recycled materials.

For environmentally conscious homeowners, the use of recycled glass is often viewed as an additional benefit.

Things to Consider

Glass media generally costs more than silica sand.

For many residential pools, the improvement in water clarity may be noticeable but not dramatic.

If an existing filter is undersized, poorly maintained or operating with inadequate circulation, replacing the media alone is unlikely to solve underlying problems.

Zeolite

Zeolite is a mineral with a highly porous internal structure.

It has been promoted within the pool industry for many years because of its ability to capture fine particles and its capacity to adsorb certain dissolved compounds.

One of the more commonly promoted benefits is its ability to adsorb ammonium ions, which are associated with the formation of chloramines under certain conditions.

While this property is scientifically valid, the practical significance for a well-maintained residential swimming pool is often less dramatic than marketing material may suggest.

In pools with good water chemistry and effective sanitisation, chloramine formation is usually managed through proper chlorine levels and oxidation rather than relying solely on the filter media.

Advantages

Potential benefits include:

• Fine particle removal.
• High internal surface area.
• Good hydraulic performance.
• Potential adsorption of some dissolved compounds.
• Long service life when maintained correctly.

Limitations and Considerations

Zeolite is generally more expensive than silica sand.

Some products require specific installation procedures or periodic regeneration depending on the manufacturer’s recommendations.

As with other premium media, the overall improvement depends heavily on the condition of the entire circulation system.

Marketing Claims Versus Real-World Performance

Pool owners are often presented with impressive marketing claims when comparing filter media.

These may include statements such as:

• “Filters to 3 microns.”
• “Crystal clear water.”
• “50% less chlorine.”
• “80% less backwashing.”
• “Eliminates chloramines.”
• “Virtually maintenance free.”

While many of these claims are based on laboratory testing under controlled conditions, real swimming pools are much more complex.

Actual performance depends on many factors, including:

• Pump sizing.
• Flow rate.
• Filter size.
• Plumbing design.
• Water balance.
• Sanitiser levels.
• Debris load.
• Maintenance practices.

Rather than focusing on a single marketing claim, it is more useful to consider how the entire filtration system performs over many years of operation.

Technician’s Perspective
One of the biggest improvements you can make isn’t necessarily changing the filter media—it’s ensuring the filter itself is correctly sized. An undersized filter with premium glass media may still struggle to maintain water clarity, while a generously sized sand filter can often provide outstanding results with lower operating pressure and reduced maintenance.

How Often Should Filter Media Be Replaced?

This is one of the most common questions pool owners ask. There is no single answer because replacement depends on many factors.

These include:

• Pool usage.
• Water chemistry.
• Frequency of backwashing.
• Environmental conditions.
• Debris load.
• Filter size.
• Media quality.

As a general guide:

*These are typical residential estimates only. Actual service life depends on operating conditions and maintenance.

Signs Your Filter Media May Need Replacing

Many pool owners assume the media is still working because water continues to circulate.

However, aging media often becomes less effective gradually, making the change difficult to notice.

Some common signs include:

• More frequent cloudy water.
• Longer recovery after heavy rain.
• Increasing filter pressure.
• More frequent backwashing.
• Shorter filter cycles.
• Reduced water clarity despite balanced chemistry.
• Persistent fine dust returning to the pool.

These symptoms don’t always indicate worn media, but they are worth investigating if the media is approaching the end of its expected service life.

Which Filter Media Would We Recommend?

There is no universal answer.

Each media has situations where it performs exceptionally well.

For most residential swimming pools:

• Silica sand remains an excellent, reliable and economical choice.
• Glass media is a premium option that may offer benefits in water clarity and maintenance, particularly in well-designed systems.
• Zeolite can be appropriate in some applications, although its additional cost should be considered against the expected practical benefits.

The most important decision is not simply selecting the most expensive media—it is choosing a filtration system that is correctly sized, professionally installed and maintained as part of an overall water management strategy.

Looking Ahead

Now that we’ve explored what happens inside the filter itself, the next section will focus on one of the most important decisions pool owners make: choosing the right filter for their pool.

We’ll discuss how pool size, pump selection, hydraulic design, surrounding vegetation, heating systems, in-floor cleaning, robotic cleaners and household maintenance preferences all influence which filter is likely to deliver the best long-term performance.

Disclaimer: The information provided in this article is intended as a general guide to help pool owners better understand swimming pool equipment and maintenance. While every effort has been made to ensure the information is accurate at the time of publication, it should not be relied upon as specific technical or professional advice. Every swimming pool is different. Factors such as pool size, construction, equipment configuration, hydraulic design, water chemistry, environmental conditions and how the pool is used can all influence the most appropriate solution. Recommendations that are suitable for one pool may not be appropriate for another. Before purchasing, modifying or replacing pool equipment, or making significant changes to your pool’s operation or water chemistry, we recommend seeking advice from a qualified pool professional who can assess your individual circumstances.

If you would like independent advice on selecting the right filtration system, diagnosing a pool problem or optimising your pool equipment, the team at SplashCraft is always happy to help.