After backwashing a DE filter, a new application of DE filter powder is added to the filter by pouring directly into the skimmer. A semi-annual breakdown of the filter is necessary to thoroughly clean DE filter grids. A DE filter requires a coating of DE powder on the filter grids. This is where the dirt gets trapped in your filter. The powder, when first added, dissolves in the pipe on its way to the filter tank. When it reaches the grids, the powder stops, coating the grid. The water passes on through the powder, then the fabric covered grid, leaving the dirt trapped in the DE powder coating.