Filters, Sand

For pools the most popular filtration is also the oldest, sand filtration. All sand filters have 2 things in common. 1) Water flows from top to bottom when the filter is in filtration mode. And 2) they all have an under drain with slots or a lateral system that allows the filtered water to pass through and holds back the sand.

Typically sand filters use special filter sand that is .45 to .55 mm (#20 silica pool-grade sand) which has sharp edges that separate the particles allowing particles to be trapped. Initially large particles will be trapped and then as the sand loads up smaller particles will be trapped.

Sand filters need the sand media to be cleaned regularly by backwashing. This is the process by which the flow is reversed on the filter and the dirt is washed to waste.