If the sand hasn't been tainted by FLOC or clarifiers you can do a deep clean of the sand-
Maddie
Deep Cleaning a Sand Filter
This post will walk you through the anatomy of a sand filter, and then provide a video at the end for how to deep clean your sand filter. The filter used in the photos and videos is a Hayward S180T top mount sand filter. The images are of a similar filter. Obviously not all filters are...
www.troublefreepool.com
Maddie