Sand Filters have the lowest filtration capability out of the three types of filter available for pools and spas. They provide filtration down to 25 - 30 microns. This will leave behind some particles that are able to be detected by the human eye. To clean out the debris that is collected in the sand filter, the sand filter is backwashed. The backwash process reverses the flow of water in the tank to remove the debris that’s studded in the sand bed. Backwashing should be completed when the PSI gauge reads 8 - 10 PSI higher than the starting PSI. Sand filters use grade #20 silica sand as the media type, although alternative media types are available. It’s recommended to replace the sand every 7 - 8 years or as needed to maintain filtration capability. Here at PoolSupplyWorld, we offer all the most reliable and popular manufacturers and brands such as Hayward, Waterway, Pentair, and many more! If you have any questions or concerns please feel free to contact us at 1-800-772-0467 or chat with us online at www.poolsupplyworld.com.