Pool Filters Explained

Part 1: Pool Filters Explained

Choosing a pool filter can be difficult. In this article, we provide information about choosing, maintaining and getting the best performance from your pool filter.

A swimming pool filter is often described as the “heart” of the pool, but that’s not quite accurate. The pump is the heart it keeps water moving. The filter is more like the kidneys. Its job is to continuously remove suspended dirt and debris from the water, helping keep your pool clean and clear.

Despite this, pool filters are one of the least understood pieces of equipment in a swimming pool. Many people assume that a filter makes the water safe to swim in, or that replacing a filter will solve every water quality problem. In reality, a pool filter is just one part of a carefully balanced system that also includes circulation, sanitation and water chemistry. When these work together, the result is sparkling, healthy water. When one part is neglected, even the most expensive filter won’t be able to compensate.

At SplashCraft, one of the most common questions we’re asked is, “Which pool filter is best?” The answer isn’t as simple as choosing the newest model or the most expensive option. The best filter depends on factors such as the size of your pool, the surrounding environment, how often the pool is used, the type of sanitising system you have and how much maintenance you’re prepared to do. The aim of this article is to help Australian pool owners understand the different types of pool filters, how they work, and what to consider when selecting or maintaining one. Whether you’re replacing an ageing filter, building a new pool or simply trying to understand why your water isn’t as clear as it should be, this guide will help you make informed decisions based on practical experience.

Why Pool Filtration Matters

Every day, contaminants enter your swimming pool. Some are obvious—leaves, grass clippings, insects and dust. Others are almost invisible. Pollen, body oils, sunscreen, skin cells, microscopic algae, airborne pollution and fine organic particles all find their way into the water.

If these contaminants are allowed to accumulate, several problems can develop:

• Cloudy or dull water.
• Increased chlorine demand.
• Reduced sanitiser effectiveness.
• Greater risk of algae growth.
• Poor water circulation.
• Higher running costs.
• Increased wear on pool equipment.

The role of the filter is to remove these suspended particles before they build up to the point where they affect water quality.

One important point that’s often overlooked is that filtration is a continuous process. Every time water passes through the filter, a proportion of the suspended particles is removed. It is repeated circulation that gradually cleans pool water over time. This is why filtration time is just as important as filter quality. Even an excellent filter cannot produce sparkling water if the circulation system only operates for a few hours each day.

Technician’s Tip
A surprisingly common mistake is reducing pump run times to save electricity. While this may lower power consumption in the short term, inadequate circulation often leads to cloudy water, algae growth and increased chemical use. In many cases, the cost of correcting these problems exceeds the savings made on electricity.

A Common Misconception About Pool Filters

One of the biggest misconceptions among pool owners is that the filter “cleans” the pool.

In reality, the filter only removes physical particles suspended in the water.

It does not:

• kill bacteria,
• destroy viruses,
• eliminate algae,
• oxidise organic contaminants,
• balance pH,
• increase chlorine levels,
• or prevent contamination on its own.

These tasks are performed by your pool sanitiser—usually chlorine, although some pools also use mineral systems, ozone or UV treatment as supplementary technologies.

A healthy pool depends on four systems working together:

1. Circulation – moving water around the pool.
2. Filtration – removing suspended particles.
3. Sanitation – destroying harmful microorganisms.
4. Water chemistry – ensuring the sanitiser remains effective and protecting pool surfaces and equipment.

Neglecting any one of these systems affects the performance of the other three.

The Science Behind It

Its important to note that water clarity and water hygiene are not the same thing.

A swimming pool can look perfectly clear while still containing harmful bacteria or insufficient sanitiser. Likewise, a slightly cloudy pool may still be microbiologically safe if sanitiser levels are correctly maintained.

This distinction is important because filters remove particles, while sanitisers such as chlorine kill microorganisms. The two processes complement one another but perform very different functions.

How Pool Filtration Actually Works

Understanding how water moves through your pool makes it much easier to understand the role of the filter. The filtration process follows a continuous cycle.

Step 1 – Water leaves the pool

Water is drawn from the skimmer box, where floating debris such as leaves and insects are collected, and from the main drain or floor suction point if fitted.

Some pools also have dedicated vacuum lines or in-floor cleaning systems that contribute to circulation.

Step 2 – The pump moves the water

The pool pump provides the energy needed to move water through the plumbing system.

Contrary to popular belief, pumps don’t “suck” water through the system. Instead, they create a pressure difference that allows atmospheric pressure to push water towards the pump while the pump pushes it onward through the filter and back into the pool.

Modern variable-speed pumps can adjust flow rates to improve energy efficiency while still maintaining excellent circulation.

Step 3 – The filter removes suspended particles

The water now enters the filter.

Depending on the type of filter installed, suspended particles are trapped by:

• a pleated cartridge,
• a bed of specially graded silica sand,
• recycled glass media,
• zeolite,
• or, less commonly in Australia, diatomaceous earth.

As the filter captures debris, it gradually becomes more efficient at trapping finer particles. However, as debris accumulates, resistance to water flow also increases.

Eventually the filter must either be cleaned or backwashed to restore normal flow.

Step 4 – Sanitisation continues

Once filtered, the water usually passes through additional equipment such as:

• salt chlorinators,
• mineral systems,
• UV units,
• ozone systems,
• heaters,
• heat pumps,
• and/or chemical dosing systems.

Only after completing this journey is the clean, sanitised water returned to the pool through the return inlets.

This process repeats continuously while the circulation system operates.

Why Flow Rate Matters

Many people focus entirely on how fine a filter can remove particles.

In reality, flow rate is equally important.

Imagine trying to pour water through a coffee filter too quickly. The filter struggles to perform efficiently because the water is moving faster than it was designed to handle.

Pool filters behave in much the same way.

An oversized pump connected to an undersized filter can:

• reduce filtration efficiency,
• increase pressure,
• shorten equipment life,
• waste electricity,
• and place unnecessary stress on plumbing components.

Conversely, a properly matched pump and filter provide excellent filtration while operating at lower pressures and using less energy.

This is one reason professional equipment sizing is so important. Choosing the largest pump available doesn’t necessarily produce the cleanest pool—in fact, it can sometimes have the opposite effect.

Looking Ahead

Now that we’ve covered the fundamentals of filtration, the next section examines the different types of pool filters available to Australian pool owners. We’ll compare cartridge filters, traditional sand filters, glass media systems, zeolite and diatomaceous earth (DE) filters, explaining how each works, where they perform best and what type of pool owner they’re best suited to.

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.