Many of us on the forum with sand filters routinely (after backwashing) add a little DE to our filters. It seems to help the filter catch more stuff. You only add enough to make the pressure on your filter rise by 1 psi. Premix it with a little water before pouring it in the skimmer. It will usually take 20-30 minutes for the pressure to rise, so wait a bit after the initial dose before deciding if you need to add a little more. It might help clear your pool faster.