Water clarity is a crucial aspect of pool maintenance, whether a job site involves a small family pool or a huge commercial vessel.
But experts agree that there’s no “magic bullet”
when it comes to filter media — each type has its ups and
downs, and is ideally suited for some situations while potentially
disastrous in others.
Here, veteran service technicians and scientists share their
perspectives on selecting filter media, and walk through the
process of assessing a pool’s filtration needs.
As many service techs know, sand is the oldest type of filter media
in the pool industry — but what’s less well known is
that it’s the oldest filter media in human history, dating
back to the baths of ancient Egypt.
Like many tried-and-true technologies, sand filtration works as
well as ever in a limited range of circumstances — but as
today’s pool circulation systems have grown more complex, and
filtration expectations more stringent, it’s no longer the
most efficient option available.
Still, sand is widely used in commercial pool systems —
particularly those with relatively slow circulation rates. In the
1950s, when the pool industry was still in its infancy, many public
pools used rapid-rate sand filters, which filtered water through a
bed of sand with a gravel substrate. This system was soon made
obsolete by high-rate sand filtration, which uses much smaller sand
particles and no gravel. Thus, most of today’s “sand
filters” are more precisely termed “high-rate sand
These filters typically use sand particles between 0.018 in. and
0.022 in. In size — often called “#20 standard silica
sand” — though some operators substitute other media
such as zeolite, or a mixture of crushed glass and gravel. Material
at this level of fineness can usually entrap particles between 20
and 100 microns in size.
This might sound tiny, but sand actually misses many particles that
would be caught by more modern filters.
Operators who choose sand filtration are often motivated by the
desire to keep costs down, or simply by the knowledge that the
pool’s bather load isn’t particularly high. In some
cases, this is a sensible decision.
However, a sand filter can bring along other costs that might not
be as obvious. As the top bed becomes caked over with debris, its
sand will sometimes start to form vertical channels, experts
explain. These channels can reduce the area where optimal
filtration is taking place because the water is mostly flowing
through the channels that have formed, instead of diffusing evenly
through the filtration media.
Another inconvenience of sand filters is that they must be
backwashed frequently — the exact timing varies according to
factors such as bather load and flow rate, but most systems require
a backwash approximately once per month. In addition, the
effectiveness of a sand filter can drop drastically if the sand
isn’t replaced at least once every five years. This process
can get fairly involved — it entails scooping large amounts
of sand out of the filter, finding a place to dispose of the
material, then refilling the filter with an even layer of clean new
In short, sand filters are best suited for applications where low
cost is a top consideration, bather loads are fairly limited, and
yearly “refreshes” are acceptable to both the site
operator and the service tech.
A traditional sand filter is composed of
a large central chamber — filled with sand and/or gravel
— through which water is circulated. A diatomaceous earth
filter’s overall design is similar, but its central chamber
is more cylindrical, and is filled with grids specially designed to
be coated with DE.
A significant step up from sand in several ways, diatomaceous earth
(DE) is composed of the skeletons of microscopic prehistoric
organisms. The complex structure of these skeletons results in much
finer filtration — down in the range of 3 to 5 microns
— than #20 sand can achieve. This fine texture, combined with
high permissible flow rates, has made DE the filter media of choice
for many of today’s service technicians.
This effectiveness comes with a price, though. First, DE is toxic
to humans, which means it’s crucial to wear facial protection
to prevent anyone from accidentally inhaling or swallowing the
substance. Care must also be taken to ensure that the powder
doesn’t contaminate nearby chemicals or equipment, where it
can cause corrosion or other unwanted reactions.
Because of concerns like these, many cities and counties also have
regulations against disposing of used DE in the street, or even
down public wastewater lines.
These restrictions have led many techs to develop workarounds.
Supporters of DE recommend disposing of used media in the
customer’s yard (after securing permission, of course) where
it acts as a fertilizer for plants. Another option is to use catch
basins, which allow water to drain away from the DE, which can then
be thrown into the trash.
Still, cleanup and disposal of DE can be nearly as messy as
cleaning a sand filter — or, in a way, even more so, given
the media’s toxic nature. And DE filter’s require more
backwashing, experts say.
DE is ideally suited for pools with high bather loads where
pristine water is a major priority. Maintenance won’t be a
cinch by any means, but proper care will ensure effective
filtration of most particles, even at high flow rates and
A major leap forward in filtration technology came with the
development of cartridge filters. Rather than using a chamber
filled with loose filter media, these filters strain water through
a compact array of pleats that catch particles down in the range of
5 to 10 microns in size — about a third the width of a human
Though their don’t catch particles quite as tiny as those
caught by DE filters, cartridge filters are more efficient,
especially in pools with relatively low bather loads and flow
rates. In these conditions, a cartridge filter with a footprint of
a few square feet can filter a volume of water in the range of 500
square feet; far more than a sand filter of the same size.
Techs also report that these filters tend to be resistant to
breakdowns and serious clogs, and are much easier to clean than
And unlike sand and DE, cartridges don’t require backwashing
or regular media replacement. Instead, all a tech needs to do is
remove the cartridge from the filter tank and hose it off; or, in
some cases, dip it in a mild muriatic acid solution to remove
particularly stubborn particles.
The downside is that if this cleaning isn’t performed
regularly, cartridge filters have a tendency to clog, especially in
pools with high bather loads, techs report.
Thus, cartridge filters are best suited for applications with low
to moderate bather loads and water volume, such as residential
pools that see usage a few times a week. If simplicity of
maintenance is a high priority, a cartridge system may be
Pool & Spa News wishes to thank the following people
for providing their expertise for this article:
• Richard Medina, vice president of
operations and engineering at Pleatco, LLC in Glen Cove, N.Y.
• Steve Boykins, owner of AquaPoolCo in Los Angeles
• John Shonfield, owner of Shonfield Pools in Los
• Scott Gleason, national sales manager at Unicel in
• Bruce Stump, vice president of sales and marketing at
Filbur Manufacturing in Buena Park, Calif.