Porpoise Diatomaceous Earth Filter Media 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 one to three microns, are trapped during the first pass through the media. All D.E. filters have internal elements that become coated with D.E. It is this combination that filters out the impurities and keeps your water clean.