Diatomaceous earth is a porous powder with microscopic openings that when magnified look like tiny sponges. Clear water can pass through these openings, but particles, as small as two to five microns, are trapped during the first pass through the media. D.E. filters have internal elements that become coated with D.E. It is this 'filter cake' that strains dirt, dust and algae from the water.
Similar to sand filters, when D.E. filters become dirty, they are cleaned either by backwashing, or regenerating and draining the clogged D.E. to the 'waste' line. To restore filtration, a fresh 'charge' of D.E. is added to the filter. For sparkling, clean pools; step up to Hayward D.E. filters.