Choosing a Swimming Pool Filter

The job of a pool or spa filter is to remove the tiny dirt particles that make the water cloudy.

Types of Pool Filters

Sand Filters

Sand filters are perhaps the least efficient of available pool filters, but they are also the least expensive. Sand filters are large tanks that hold hundreds of pounds of special pool sand. As the dirty water filters through the mass of sand, the sand's sharp edges snag the dirt.

Sand filters can remove dirt particles down to about 20-25 microns in size. They are efficient enough to keep most pools clean.

Maintenance can be tedious. In order to clean them (they need cleaning about once a week), you have to backwash. Backwashing is when the water flow is reversed and clean water washes through the filter. This water is ultimately wasted. Sand filters are not a good choice in places where there are water restrictions.

Diatomaceous Earth Filters

Diatomaceous earth is a powder made of billions and billions of fossilized plankton skeletons. The inside of a diatomaceous earth filter holds a number of cartridges coated with the stuff. It works very well to catch and hold dirt.

They are the most expensive type of pool filter, and they get the water cleaner than other types of filters. Diatomaceous earth filters can catch particles as small as 3-5 microns.

Maintenance can be demanding, however. Most of them require back washing,
and this isn't always enough to get them clean. You may have to remove the grids and discard the used diatomaceous earth. This
can be a pain since some towns classify it as hazardous waste, so you cannot simply throw it away.

Cartridge Filters

A cartridge filter is a tank that holds 3 or 4 cylindrical cartridges. Each cartridge is made up of some fabric like polyester that catches the tiny particles of dirt and holds them until you clean the filter.

Cartridge filters can handle dirt as small as 5-10 microns in size (anything smaller than 35 microns is impossible to see with the naked eye). Cartridge filters are usually less expensive than diatomaceous earth filters but cost more than sand filters.

Cartridge filters require very little maintenance. You
can sometimes get away with just hosing off the cartridges a few times during the swim season. You may need to soak the cartridges in a cleaning solution. At the worst, you replace the cartridge (they are relatively inexpensive).