I have a 15k IG pool with a pent air 420 cartridge filter and a pent air 1hp pump. the normal pressure was about 5-7. this past year the pressure rose @ 25-30 and the circulation decreased. I cleaned tha filters which broght the pressure down to normal levels, but within the week the pressure rose the chemicals were good and the pool looked good. I bought new filters. everything was fine for the first 3 weeks then the pressure rose again 10- 15. I cleaned the filters again and with the sasme results. I feel I'm cleaning the filters to often. when the pool was new 4 yrs ago i only had to clean the filters once a season. any help would be great.