Diatomaceous earth and cartridges each do an excellent job of keeping pools free of particulates. However, there are cases where it makes sense to choose one filter medium over the other.
Here’s a look at where each shines.
Jim Romanowski is a DE guy. “I really love DE filters because
they just filter so much better,” he says. But several years
ago, one of the commercial pools he services was undergoing a
remodel and the contractor specified three high-rate sand filters
in the plans. “I questioned this, but decided the best way to
know their efficiency was to give them a shot in the
The customer found he was using more electricity and chemicals
than he had previously. Then an automatic chlorinator failed and
the resulting green pool took a long time to clear. Shortly
thereafter, Romanowski, who owns Pool Perfection Pool Service in
Huntington Beach, Calif., pulled out the sand filters and replaced
them with new DE filters.
DE filters are among the most effective ways of clearing solids
from pool water, removing particles as small as 4 microns in
diameter. Sand filters, on the other hand, will remove particles as
small as 25 microns and cartridge filters will remove particles as
small as 15 microns. To put it in perspective, a grain of table
salt is about 100 microns in diameter.
That fine filtering appeals to Scott Overholt, owner of Complete
Pool Care in Hemet, Calif. “I’ve had a number of
customers who I convinced to use DE filters,” he says.
“The DE filters work much better on catching the algae.
You just backwash or clean it after that, especially in a pool
that’s been neglected for a while,” Overholt says.
Romanowski also appreciates the bounce-back ability of a pool with
a DE filter. “With a DE filter, you can shock it, backwash
it, clean the filters and overnight you can get a good-sized pool
clean again. Sooner or later, something’s going to go wrong
and a pool with DE filters that has something wrong will recover
much faster,” he says.
DE is made of fossilized skeletons of prehistoric plankton that
act like tiny sponges. It’s introduced into the pool by way
of the skimmer, sometimes in a slurry. A good rule of thumb is to
add 1 pound of DE per 10- to 12 square feet of filter area. The
media runs through the system and adheres to a grid, or septum, in
the filter. There, the DE traps particulates.
Although DE is perhaps the most efficient filtering media, it
has drawbacks. The first has to do with safety. Service technicians
must guard against inhaling DE while they’re adding it to a
pool. Each tiny skeleton has sharp edges, which can cause problems
in the lungs. Techs are advised to use a dust mask when pouring DE
into the skimmer.
The filters must be backwashed and recharged periodically with
fresh DE, usually when it’s 8- to 10 pounds of pressure over
the reading taken right after the filter’s cleaned.
“Every system’s different. You get to know each
swimming pool’s eccentricities,” says Bob Foutz, owner
of Purity Pool Service also in Huntington Beach. “I had a
condo pool that if it was at 19 pounds [of pressure at the filter],
I knew it would make it through the weekend. If it was at 20 or 21
pounds, I knew I had to backwash on Thursday; the pool
wouldn’t make it through to Monday.”
In addition, a full cleaning should be performed at least once a
year, with some techs recommending services be done at the
beginning and end of a swimming season. And when the filter grids
are cleaned, care must be taken to ensure that the old DE
isn’t washed into a storm drain. “I’ve had some
really old pools that had DE filters but no backwash line, so the
water just ran out into the street, and that’s
illegal,” Foutz says. “So when their filters gave out,
I talked them into switching to cartridge because their backyard is
better suited to that.
“In a cleanout, I backwash first to get as much out of the
filter as possible. If it has a backwash line, you can sometimes
clean the grids right in the tank, so all the dirt goes right into
the sewer system. If you can’t do that, I scrape as much of
the muck into a bucket as I can, then I’ll clean it in the
bushes or the grass.”
The used DE won’t hurt grass or plants, but service techs
should check with the customer before washing DE into greenery. It
also can be thrown in the trash.
Another issue with DE filters is that the filter grids
themselves can become torn or clogged and require replacement.
“Commercial accounts go through a lot of grids,”
Overholt says. “The cloth seems to decay faster with more
chemicals going through the system.” If DE starts showing up
in the pool, it might mean that one of the filter grids is
Complexity is another characteristic of DE filters. This can
work to a service tech’s advantage. “They have the most
moving parts of any filter, so they break down more often.
There’s more money to be made,” Foutz says.
Cartridges don’t filter quite as small particles as DE, but
they have the advantage of being simpler to use. There is no
backwashing with a cartridge filter. Instead, the element is
removed from the filter, hosed off, cleaned and replaced in the
filter. If there is a heavy mineral buildup, the element can be
soaked in a solution of filter-cleaning product. Cartridge filters
also have the advantage of having the smallest footprint of any of
the three filtering methods. This can be crucial when only a small
amount of space is available for the equipment pad.
“There is a shift moving toward cartridge,” says
Javier Payan, who owns Payan Pool Service in San Diego. “We
do a lot of work in coastal communities with small properties and
there’s really no place to clean a DE filter. Some customers
want us to take the filter off-site to clean it.”
So for many of those customers, Payan recommends a switch to
cartridge filters. Most of those clients have accepted the switch.
“We tell customers they will not notice the difference,” Payan says.
Ease of use
Jerry Wallace, president of Swim Chem in Sacramento, Calif., has
been sold on the advantage of cartridge filters for some time.
“It’s a nice sell; they’re clean, they’re
easy to use,” he says. “The filtering efficiency has
improved dramatically since they were first introduced. The
capacity is pretty good — you can have pretty long run cycles
Other than an occasional cleaning, the only maintenance is the
replacement of the filter element. And modern elements can last a
long time if they’re well cared for.
“It depends on how well they’re taken care of,”
Wallace says. “If they’re not properly sized, if the
flow rates are really high, if the pressure increases because
they’re not cleaned often enough — all that has an
effect on the life expectancy of the cartridges. We usually get
three- to five years on a cartridge, and sometimes they go longer
Stricter dumping regulations are causing some pool service techs
to switch to cartridges. “When they imposed new discharge
regulations and started fining pool guys, it became more of an
issue,” says Bill Peck, owner of William Peck Pool Service in
San Diego. “Cartridge filters, if sized properly, are usually
a better option than trying to find a place for backwash
Wallace sees some customers switching from DE to cartridge.
“We’re still doing a few conversions,” he says.
“A lot of our customers have had their diatomaceous earth
filters replaced already by us or by somebody else. There are still
some DE filters out that that we’re changing to a cartridge
Pool owners who switch from DE to cartridges usually don’t
see a difference in their water quality. “I wouldn’t be
afraid of the change,” Wallace says. “My dad started
the business way back when and we started with DE. When cartridges
first came out, we didn’t push them that much. But over the
years, as the technology improved, the filtering capabilities of
the product improved, and now with the high-capacity filters,
we’re definitely believers.”
Wallace pointed out that cartridges can even bring a bonus to a
pool owner. “The thing that makes it real easy for the
consumer is if they’re do-it-yourselfers; you can have a
second set of cartridges and they can clean them at their
leisure,” he says.