Mar 07, 2016 · Try the very hottest wash with no detergent at all or maybe a handful of soda crystals. If you are in a hard water area it might be worth using a cleaner for washing machines in a hard water area, like Calgon or a supermarket own brand. It's maybe 2 years old. Very hardwater area. I can literally Hoover them out.
A sand filter is basically a large tank filled with poolgrade sand, which is coarser than regular play sand. Water enters the tank through an inlet at the top, and gravity pulls it downward, removing impurities that get lodged in the sand. At the bottom of the tank, the water enters the laterals, which have tiny perforations that keep out the sand.