I recently purchased a home with a concrete pool and a cartridge filter. I have owned homes with pools before but always vinyl liners and sand filters. Despite having a new cartridge filter I find my pressure rising to 30-35 psi each day and my water barely circulating. I have been giving the cartridge a thorough cleaning and the pressure drops down to about 10-15 psi but within a day or so its back up again. I have even put a filter bag on the skimmer to try and catch some of the dirt and debris without success. With a sand filter I would just backwash and go on but the cartridge issue is giving me fits. I am afraid I am going to ruin the cartridge with repeated cleanings. It generally doesn't look that terribly dirty when I remove it. What else could be causing the pressure issues? Thanks!