Diatomaceaous Earth 50 Lb Bag

This widely available, inexpensive powder is mined and is actually the microscopic fossilized exoskeletons of tiny Diatoms, an ancient, sub-aquatic creature. Under the microscope, these skeletons appear to be tiny sponges. 

This is where the dirt gets trapped in your filter. The powder, which is added at your skimmer, dissolves in the pipe on its way to the filter tank. When it reaches the grids, which are covered with a nylon type of fabric, the powder stops, coating the grid. Grids are also called Elements or Septums. 

The water continues to pass through, first through the powder, then the fabric-covered grid. As the water passes through the D.E. and enters the grid it leaves the dirt, trapped in the D.E. powder "cake" or coating.