I''l try to answer this question another way.
Driving the filter with a 900 gph pump on a freshwater 125 gallon tank, with live plants and approximately 60" of fish (cory & porthole cats, tetras, rasboras, gourami, angelfish, otocinclus, rams, kribensis, African butterfly), feeding dried and frozen food. In the first year after setting up the tank I found I had to flush the filter every two months and was able to squeeze close to six months on the cartridge and eight months on the polyester pads in the center. 25gal water changes were performed every one to two weeks. The tank has now in it's second year and I added a sponge filter over the intake as a pre-filter. Currently I am flushing the filter about every month and getting about four months per cartridge and six months on the center pads. I still feel this is a great filter canister. In my system, a new cartridge develops a back pressure of about 3.5 psi, when it gets to 5 psi its flow falls to 1/2 or less. and 5.5 to 6 psi the flow is about 1/4 of normal.