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.

Sand
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 filters.”

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 sand.

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.

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 temperatures.

Cartridge
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 hair.

Though they 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 sand filters.

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 ideal.

Source: Ben Thomas- Pool and Spa News | 1.27.2012