All pools, whether they are diatomaceous earth, sand or cartridge filters, have a pool pump. The pump is the motor for the filter that provides the suction power from the pool skimmer through the filter and back out the pool again. If the pool filter's pressure gauge is reading 8 to 10 psi above its normal reading, it needs to be cleaned. Part of that cleaning process is bleeding the filter to relieve the internal pressure the pump built up while operating.
Turn the filter off. Locate the filter's pressure gauge, which is typically on the top or side of the filter tank.
Open the release valve that is next to the pressure gauge by turning it counterclockwise. The pressure gauge and air release valve should be part of a "T" valve on the filter tank with a pressure gauge.
Listen to the hissing sound coming from the filter tank. This is the air pressure being released from the filter. If you are cleaning your filter, now is the time to backwash while the valve is open. Backwash the filter if necessary according to your manufacturer's guidelines.
Close air release valve by turning it clockwise when the hissing sound of air stops coming from the filter. Restart the filter and the pressure will restore to its normal reading.