For years and years I dutifully dumped my sand from my Proline sand filter and refilled it at opening. I recently switched to Hayward becasue the parts are easier for me to get. The guy who delivered it told me I didn't need to dump the sand. In fact he said with Hayward, it is difficult to do.
Please chime in with a discussion of this. I have created in 15 years a small beach next to my pool with all the years of sand!