Cartridge filters do an excellent job of maintaining clean pool water. However, they will continue to keep the water clean only if the cartridge itself is well-maintained. When it comes to taking care of a cartridge filter, the one task that you must perform regularly is cleaning the filter. Unfortunately, cartridge filters don't have a "Backwash" setting, because they were not built for reverse water flow. Therefore, to backwash the cartridge you must take it out and manually clean it.
Turn off the filter, shut the valve from the filter outlet that goes to the pool inlet and shut the valve that goes from the skimmer to the pump inlet. If you don't have valves at these connections, insert a plug into the skimmer to stop the flow of water into the pump and another plug at the pool inlet to prevent the water from flowing back into the filter housing.
Loosen the air valve on top of the filter to allow air to enter into the cartridge filter housing.
Open the filter drainage valve. The drainage valve is located at the bottom of the filter housing. The goal is to empty the trapped water from the filter housing.
Take the top off the cartridge filter to access the cartridge. Depending on the type of cartridge filter, you may have to unlock a safety latch. Check with your manufacturer's instruction manual for directions on how to unlatch and remove the top of the filter housing.
Lift the filter from the housing and hose it off with a garden hose. It's best to set the garden hose to the most powerful setting to remove the hard-to-remove debris caught in the cartridge filter.
Hose the inside of the filter housing too. Make sure to hose the top and the bottom to remove all dirt remnants.
Replace the cartridge filter and place the top on the filter housing. Make sure the filter housing is locked.
Close the drainage valve and open the filter outlet valve and the pump inlet valve (or, unplug the skimmer and pool return if you plugged it earlier).
Turn on the filter and wait for water to spray through the open air valve. Once the water begins to spray out, shut the air valve. Your cartridge filter is now ready to clean your pool water.