Pool Filtration

With the large volume of water employed by swimming pools for leisure use, it is not practical to fill up and drain swimming pools before use and after use.  Swimming pools instead are equipped with a pool filtration system to keep the pool clean and sanitary for use.

The pool filtration system consists of swimming pool pumps, pool filters, drains, skimmers, return fittings, and other optional equipment and fittings.

The pool pump circulates the pool water in and out of the pool.  From the pool, water exits through the drains and into the pumps to the filters, and then back again through various return fittings installed.  The proper performance of the pool pumping system is dependent on the size of the pool and the expected use of the pool.  For residential pool use, it is common to size the pool pump to be just powerful enough to circulate the whole volume of the water for 8 or 10 hours.  For commercial pool use, where we can expect more swimmers and dirt, 6 hours for full circulation is more appropriate.

The pool filters are the primary cleaning mechanism for the swimming pool.  They should be sized according to the volumetric flow (gallons per minute or liters per hour) capacity of the pool pumps.  Sometimes, pool contractors or equipment suppliers may use undersized pool filters to reduce contract prices.  Unfortunately, this commonly leads to pool filter failures and are not considered normal operation and not applicable for warranty.

There are different kinds of pool filters, among them:

  • D.E. Filters (Diatomaceous Earth-using filters)
  • Sand filters
  • Cartridge filters

D.E. Filters use diatomaceous earth for filtration.  Diatomaceous earth is a chalky substance that has high porosity.  The surface areas of the cloth-like grid elements of D.E. filters are caked with D.E. powder to provide effective filtration of very fine particles.  Depending on your filter model, grid elements can either be individually replaced or changed as a whole set.

Square feet of filter area Pound of Diatomaceous Earth
5 0.5
10 1.0
15 1.5
20 2.0
30 3.0
40 4.0
50 5.0

Sand filters use silica sand or zeolite as filtration media.  While providing effective filtration, sand or zeolite are much cheaper operationally than D.E. powder.  Unlike D.E. filters which use diatomaceous earth as consumable, little sand or zeolite needs to be replaced once a sand filter is initially setup.  Thus, sand filters have become popular as a filtration method for swimming pools.

Size 20 silica sand is used for sand filters.  Common sands that can be excavated from beaches or river beds cannot without proper selection be used for sand filtration.

Zeolite is another medium that can be used for sand filters.  Though they cost more than silica sands, a sand filter using zeolite requires half the mass of silica needed for an all-silica sand filter.  Thus, the use of zeolite leads to investment savings.

Silica and Zeolite requirements for sand filters
Tank Diameter Filter Area (approx. sq ft) Sand Zeolite
19" 1.92 150 lb 75 lb
21" 2.46 200 lb 100 lb
24" 3.14 300 lb 150 lb
30" 4.91 600 lb 300 lb
36" 7.06 900 lb 450 lb