Ok I had not backwashed in a while and the pressure was up to about 15, which is about 8 over clean filter. So I cleaned it out and it only went down about to about 10 which is not usual. Usually after a backwashing it goes down to around 5. I let my pool go so I knew I had some algae so I started the shock process. Raised my FC up to shock level and after a few days or so the pressure was back up to pre backwash and very ligh pressure coming out of the jets. So I backwashed again today to maybe get out whatever was in there and my pressure only went down to around 10 again which is 5 more than what normal was when I did al prior cleanings. When I was backwashing the water never came out dirty. It was clean from the very first backwash. I tried about 5-6 more times with backwashing and back to pump and each time the water came out clear. Every other time in the past I have seen DE come out when backwashing. After this backwashing the pool went from semi clear to cloudy. I figured that was just from backwashing and pumping into the pool. So I added more DE and there is no DE on the bottom of the pool so it does not appear there is a leak or tear in a filter. My filter is about 20 years old or so and I have it sealed off to where when next time I open it up it will need to be replaced as part or almost impossible to find. I have been to 2-3 pool stores with 1 of them being a mom and pop store and trust his judgement completely.
So does anyone have any reason why this may be happening? Do you think it may be time to replace the filter?