Sand filters for swimming pools: why they’re needed and current possibilities

What is a sand filter for pools?

Filtration systems are one of the most crucial components of a pool’s water treatment ecosystem. In charge of removing impurities, this equipment’s role is to ultimately make water suitable for swimming or bathing.

The filtration process is as follows: pool water is distributed inside the filter, so that it flows through the chosen filter media found inside. It’s precisely this filter media that retains dirt particles which would otherwise be suspended in the water, thus removing them from the liquid. Because of this, the choice of filter media is crucial.

All made of granulated materials, there are many types of filter media that operators can choose to include as part of their filtration process. These include:

• Sand or glass. As part of a sand filter for swimming pools, this remains the most popular option for its efficiency and low maintenance needs.
• Cartridge filters. This is a replaceable option that is often preferred for residential pools because it requires very low water consumption.
• Diatomaceous earth. Paired up with a high-performance filtration system, these can remove dirt that may not be visible to the naked eye.

An efficient and sustainable filter media remains a key part of filtration systems. In fact, both choosing the best filtration technology and the most adequate filter will make sure the pool operates properly and minimize the need to use excessive chemicals for disinfection.

In this decision, the different types of filter media must be considered, along with the following three rules:

• The greater the height of the filter media, the higher the likelihood that dirt particles will be trapped.
• Different filter media also present different granulometries , meaning smaller granulometries have a greater capacity to trap particles.
• A smaller granulometry clogs up more quickly, so it needs to be backwashed more frequently.

Sand filters for pools: the main characteristics

When it comes to efficient pool filtration systems , sand is without doubt the most commonly used media. As a filtration media and due to its irregular shape, sand is able to retain any dirt present in water as it passes through its pores.

The most common choice for pools is a layer of silica sand, composed of granules sized between 0.4 and 0.8 mm. To achieve optimal performance, this combination is placed on top of an underlayer of gravel, which is thicker than the sand.

A multilayer combination of anthracite and silica sand also stands out among efficient swimming pool filter media. In this case, anthracite is layered on top of silica sand, as it is less dense but has a higher granulometry. The result involves the anthracite trapping the larger particles and letting the smaller ones trickle down to the sand. Dirt is therefore spread across two layers, overcoming a common issue in single-layer systems, where dirt concentration in the first stretch of sand makes the system require more frequent backwashing.

While both media remain key options as part of a filtration system for pools, it must be noted that sand requires maintenance in two areas. On the one hand, maintenance must ensure channels don’t form in sand, as this can result in the water returning to the pool without being filtered. On the other hand, maintenance must take the sand’s capacity to trap bacteria and microorganisms into account, ensuring these don’t then proliferate inside the filter.

There’s also another efficient alternative in filter media that makes an increasingly widespread choice: glass. As a filtration media, it’s proven efficient in avoiding canals or lumps and clogging on the first stretch of the filter media.

Because of its flat, even surface, glass allows for a better distribution of trapped dirt, which spreads across the whole of the filter bed, reducing the generation of germs and biofilms in the filter. As such, it’s able to guarantee great filtration results with fewer maintenance and backwashing needs, thus providing savings on water, energy and chemical products. It’s also an environmentally friendly option as the glass is recycled, with the added plus of its outstanding durability and resistance.

All in all, these multiple options constitute an advantage for pool operators. They can choose the one that best suits its pool project and generate outstandingly clean pool water with fewer associated costs and maintenance.

The importance of proper sand filter maintenance

Filters in use tend to accumulate traces of lime, organics and other sediments, which gradually adhere to the filter media, hindering their work and lowering their performance.

In time, this accumulation can lead to undesirable situations such as a higher consumption of chemicals or water, increased turbidity in water or unpleasant odors and organic contamination.

In order to avoid these, there are a number of actions that operators must take into account and perform:

• Backwashing. This process makes water currents flow upwards, with the aim of sweeping away the particles of dirt trapped in the filter media to later remove them. Backwashing can be performed using water from the pool, the balance tank or by recirculating the filtered water back to the filter to be backwashed. It’s usually performed every two weeks or once a month, depending on the pool and the filtration system. As we’ve seen, the choice of filter media can play a key role in more efficient backwashing and, as a result, minimising costs.
• Air scouring. An alternative to backwashing, it reduces water consumption and is able to clean the filter media more efficiently. In order to do this, air is injected through a special connection at the bottom of the filter (or at the backwash water inlet), a process through which only electricity is consumed (as water is not needed).
• Filter media changes. Another key maintenance step for a swimming pool filter is checking the state of the filter media and ensuring that the bed depth is right and that it expands as expected when backwashes are performed. So, it’s important to change the filter media whenever it is needed.

How to pick the right filtration system

As we’ve seen, the choice of filter media can indeed be a key decision when exploring optimised systems for pool maintenance and cleaning.

As such, operators must ensure they look into all current possibilities, including sand filters for pools, as well as glass options, to ensure their installations are as efficient as possible.

The help of professional pool designers and engineers will prove invaluable in suggesting the most efficient options and picking the right systems, all taking into account each pool project’s needs and possibilities.