From time to time, an in-ground pool filter needs cleaning. This could be when the pump gauge is close to redlining, or when the sand in the pump is dirty. If the pool water level is high, for example after a storm, you can backwash the filter and remove excess water.
Add water if the pool level is not more than halfway on the skimmer opening. Turn off the water heater about 15 minutes before you are ready to backwash. Open the drain valve, then close the skimmer valve on the pump. When the water has cooled, turn off the pool pump.
Close the drain valve. Remove the pump basket and any debris in it.
Turn the pump lever to "backwash." Check that the backwash hose is connected and rolled out to direct water away from the pool. The air-relief valve, located on top of the pump filter, should be opened.
Turn the pump on and open the drain valve. After the water starts flowing, open the skimmer valve so that more water flows out. When you have established a good flow, close the air-relief valve.
Allow the pump to run for about seven minutes. Monitor the water in the sighting glass until the water runs clear. Turn off the pump at this time and move the lever to "rinse." Turn the pump on again for about a minute. Shut off the pump when done.
Turn off the pump and move the lever to "filter." Turn the water heater on. Test the water with a pool test kit to see if the chemicals need adjusting, then adjust accordingly.