DLS aka Dual Layer Spiral is used in aquarium wet dry filters as an aquarium bio media. DLS bio media a woven plastic mesh that allows for the colonization of beneficial bacteria. The randomness of the weave leaves open spaces for atmospheric oxygen to interact with the oxygen hungry bacteria making is far more effective. DLS media is rolled together with a white filter media that aids in the removal of debris. This reduces the debris from settling at the bottom of your wet dry filter. We offer Single Roll DLS rolls as well as our DLS Combo Kits that include 3 DLS rolls and 3 DLS Pre Filters. Select the DLS that is sized to your aquarium.