Sand filters

- keeping the water cleanSand filter digram

Pool water is filtered when it is pumped through a bed of sand in the sand-filter

Beach, river or building sand is hopelessly inefficient in a sand filter as it is ‘round’ in form from being rolled in water, which removes the sharp edges

                                                             Sand Filter Layout  

Sand-filter sand, called Silex, is crushed from silicate rock, producing sand grains with very sharp edges

The sharp edges and smooth faces of these tightly-packed cubes leave microscopic channels for the water to pass through and it is the size of these channels that determines the size of particle that the sand-filter can trap and hold

New Silex is quite efficient as a filter medium but, over time, backwashing damage the media by bashing it around when the filter bed is 'fluidised'; chipping microscopic flakes off.

These microscopic particles are much too small to be caught in a filet, and too small to sink to the floor of the pool. They are constantly re-circulated through the filter, eroding tiny pits in the faces of the grains and smoothing the sharp edges; therefore efficiency will fall off.

The filter will become unable to trap the smallest particles with the result that the pool water will become cloudy.

Cloudy water can be corrected with flocculant but, with an inefficient filter, the problem will gradually return.

Jolly GelJolly Gel will catch the microscopic particles by contact and double the filter media life.

The best course of action is to change the sand in the filter and to fit Zeoclere-30Zeoclere-30 as an alternative filter media. When Zeoclere-30 is used in conjunction with Jolly Gel the filter media will last for 10+ years.


Changing the filter media is an unpleasant job at best; usually involving a couple of sweaty hours crouched uncomfortably over a filter filled with what can best be described as gritty, sterile liquid sewage.

If you’d like to do this job yourself you’ll find instructions here.

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Ken Walker - MyPoolGuru©