Let’s Talk Pool Filters: “What Do You Want Removed?”

Keep your pool looking good, smelling nice, and feeling silky soft with the right water filtration. Understanding how different pool filters work makes it easier to choose the right one for your pool.

It’s A Trap: Your Filter’s Job

The filter traps all the particles that pass through the skimmer basket and the hair-and-lint pot. Any dirt particles that pass through your pool’s pipes are sifted out by your filter when the cleansed water continues back into your pool. All the fine dust, dirt, and sand particles are removed from the circulating water.

Interestingly, as your filter traps more debris and becomes dirtier, it actually becomes more efficient in trapping smaller and smaller debris.  Filters help keep your pool water looking beautifully blue and crystal clear. Remember though, just because the water looks clear doesn’t always mean the water is sanitized and pure.

Filters remove solid particles from your swimming pool water. However, you do need to be aware; filters do not remove dissolved contaminants, such as oils, bacteria, or disease-causing pathogens.  When it comes to that phase of keeping your pool clean, you need a good chemical maintenance program—either by using chlorine, running an ozonator, or better still, a mineral-salt-fed chlorine generator.

Size Does Matter: It Is All About The Microns

When it comes to filtration, the smaller the particle removed the cleaner your water. The best filters remove impurities you cannot see with the naked eye—but you might notice if there were enough impurities to make the water cloudy. To measure impurities, a unit called a micron is used. A micron is a unit of length equal to one millionth of a meter (1/1,000,000 m), or 0.0000394 of an inch. The human eye can see as small as about 35 microns without magnification.

To help you understand the micron better, here are the thicknesses of some common things:

  • One inch equals 24,500 microns
  • Human hair is between 50-70 microns thick
  • A grain of fine beach sand is about 90 microns
  • Pollen is between 30-50 microns thick
  • Ragweed is between 17-23 microns thick
  • Typical atmospheric dust measures between 0.001-10 microns

Swimming pool filters are rated according to the size of microns they capture. The smaller the particles it can remove from the water, the lower the micron rating and the more efficient the filter. The smaller the particles being removed, the cleaner the water becomes. The cleaner the water, the more enjoyable the pool is.

Filter Types

Below you’ll note descriptions of the three most common types of swimming pool filters. Once you understand the advantages of each, then you can consult with a Certified Pool Professional as to which filter system best suits your pool. The three types of filters are:

  • Diatomaceous Earth (DE) filters
  • Cartridge filters
  • Sand filters

The Water Polisher

Diatomaceous Earth (DE) filters can strain out particles as small as 5 microns. DE is a white powder made from the skeletal remains of sea creatures, called diatoms. DE filters are constructed with internal grids. The DE coats the grids thereby forming a filtering mesh that removes any tiny pieces of debris in the water.

The Popular Cleaner

Cartridge Filters strain out particles as small as 10-20 microns. Cartridge filters are the newest of the swimming pool filters and are also the simplest to maintain, which is why they are so popular.

Cartridge filters closely resemble a car’s air filter (pleated polyester cloth), except that pool filters are much larger. As water passes through the pleated material, dirt particles and debris are trapped in the pleats.

Cartridge filters are available in a wide range of sizes, depending on the size of your pool.  When properly sized, they don’t clog up as quickly and more water flows through them (more opportunity to filter out debris).  If a cartridge filter is sized right, it may be able to run the entire season without cleaning.

The Trusted Age-Old Filter

Sand Filters can strain out particles as small as 20-40 microns. A sand filter is the oldest and simplest filter in use. As far back as ancient times, sand was used to filter the famous Roman baths. Pool water passes through tiny openings in the sand. Dirt and other debris are trapped in the jagged edges of the sand particles, allowing clean water to pass through.

Filter Maintenance

DE Filters

The DE filter may be partially cleaned by backwashing (reversing the flow of water through the filter). The filter grids must be re-coated with new filter media (DE) after each backwashing. Since backwashing does not remove all of the dirt and debris from the filter, it is recommended to annually open the filter and chemically clean each grid individually.

There is a cost for media and periodic maintenance.  Because DE should not be disposed of into streams or sewers, most communities require a separate vessel to capture the backwashed DE and dirt in a bag for proper environmental disposal.

Cartridge Filters

Cartridge filters are also designed to run at lower water pressure than sand or DE filters. The lower pressure puts less backpressure on the pump, often allowing you to downsize your pump for energy savings.  A new cartridge filter will start to strain out particles at about 20 microns, but can go down to as low as 5 microns. Generally these filters have to be cleaned once or twice a season by simply hosing them off.

Sand Filters

Sand filters have the highest micron rating (other filters trap smaller debris).  They start out at about 40 microns and go down to 20 microns over time—as with all filters, sand filters clean better the dirtier they get.  The only way to clean a sand filter is by backwashing. A good sand filter can go years on backwashing alone.  There are no grids to clean and no DE or sand to add—just backwash and go.

Do Your Own Research, Then Get A Professional Opinion

It always helps to have a basic understanding of filters, so your discussion with a Certified Pool Professional—such as those at B&B Pool and Spa Center—can be fruitful and, most important, money-saving!