When the pressure gauge rises 8-10 pounds above normal operating level on your sand or diatomaceous earth filter, it is time for a backwash.

To perform a backwash, shut off the pump and move the multiport valve to the backwash position.
Run the pump for about a minute or until the sight glass runs clear.
Shut off the pump and move the multiport valve to the rinse position.
Run the pump for about 15 seconds or until the sight glass runs clear.

For diatomaceous earth filters, repeat the backwash/rinse cycle 3 times.

Return the multiport valve to the filter position and run the pump. Your backwash is now complete.

For diatomaceous earth filters, you need to replenish the diatomaceous earth powder washed away from the backwash. For regular backwashes as explained above, 3-4 pounds of diatomaceous earth powder must be put into any skimmer and swirled until fully dissolved. For new installations or after the filter has been taken apart and cleaned, divide the square footage of the filter by 7 to calculate how many pounds of diatomaceous earth powder is required and dose accordingly.