The three most popular types of filtration currently in use in residential pools and spas are high rate sand, cartridge, and diatomaceous earth (DE). Each method of filtration is explaned on this page.

High-Rate Sand
The oldest and most popular method of filtration is sand.
Sand filters share two things in common:
1) When in filtration mode, water always flows from the top to the bottom.
2) They all have some sort of lateral or under drain with slots to hols back sand while allowing clean, filtered water to pass through.

High-rate sand filters use special filter sand, normally .45 to 55 mm (also known as pool grade #20 silica sand), because it has sharp edges that serve to seperate particles, allowing filtration to take place. They operate on the basis of "depth" filtration; dirt is driven through the sand bed and trapped in the minute spaces between the particles of sand. Initially, a clean sand bed will remove larger particles, and then, as the bed starts to load up, it will remove finer particles.

Cleaning of the media, or sand bed, is accomplished through reversing the flow through the filter, to the "waste" line. This is known as backwashing.

Suggested Filtration Rate

When water passes through a cartridge filter, dirt is screened out to the surface of the cartridge element. When clean, the element will trap larger particles, with finer particles being filtered out as the pores of the element become clogged by the larger debris.

The cartridge element can be removed and cleaned by pressure washing inside and out with a garden hose.

Diatomaceous earth (DE)
Many pool professionals consider D.E. filtration to be the finest, because it is capable of removing smaller particles than either sand or cartridge.

Diatomaceous Earth ia a porous powder with micro-scopic openings, that, when magnified, look like tiny sponges. Clear water can pass through these openings, but particles, as small as one to three microns, are trapped the first pass through the media.

All D.E. filters have internal elements that become coated with the D.E. I is this "filter cake" that strains the dirt, dust, algae and some forms of bacteria from the water.

Similiar to sand filters, when a D.E. filter becomes dirty, it is cleaned either by backwashing the clogged D.E. to the waste line or regenerating and draining. To restore filtration, a fresh "charge" of D.E. is added to the filter.

Water Chemistry
Whatever method of filtration is selected, it is important to remember that filtration alone does not keep water looking its best. Proper water chemistry must be maintained for safe, clean water. Most pool owner complaints are directly related to water chemistry or improper sizing of filters and pumps rather than equipment failure.