DE filters, formally known as diatomaceous earth, uses a granulated form of sedimentary rock to collect dirt and debris that is too small for a skimmer basket to catch. Cleaning your filter involves the process of backwashing and should be instituted as part of regular pool maintenance. A clean filter in combination with regular chemical maintenance is key to keeping your swimming pool water crystal clear.
Backwashing your DE filter is the process of flushing out the DE, or earth, from your filter and replacing it with a new clean DE. Through time the DE becomes dirty from collecting dirt and debris and becomes less effective in collecting material. Dirty earth can cause a loss in filter pressure, and particles can escape through the filter and back into your pool water.
How Often to Backwash
The filter should be backwashed once per week and replaced with clean earth. Most DE filters need 1 qt. of clean DE to operate efficiently. You do not want to add more earth than necessary because you risk clogging the filter, which is a critical component of pool maintenance and should be performed consistently.
How to Backwash
Turn your filter off, and open the release valve at the bottom of the filter to flush the old earth. The earth will appear dirty and green, and you should see small black particles of dirt and bugs, mostly gnats. Leave the valve open until the water runs clear. Pump the filter handle 10 times while it's draining to help loosen the earth. Turn the valve off, and pump the filter handle five times to build up the pressure. Turn the filter on, and add the new DE slowly through the pool skimmer.
Other Times to Backwash
Get in the habit of backwashing the filter after you vacuum the pool. Most of the debris collected during the pool vacuuming process gets collected by the earth, thus making it dirty. If you choose to vacuum the pool once a week, backwash the filter routinely afterwards. Run the filter after a bad rainstorm in which winds were swirling and lots of small debris was blown into the water. Backwash the filter several hours later to flush the dirt collected from the filter.