Canister Filter Head loss

I'm putting an aquarium filter system together and I was thinking of using canister filters for the last stages. While walking through Lowes I noticed the canister filters for household water filtration and thought that they were cheap enough and easy enough to use. Now I'm trying to make a system curve to size my pump and I'd like to figure out the equivelent length of pipe or the head loss that one of these filters represents.

I suppose I could use a sudden expansion and then a sudden contraction, but what about the filter media itself (one of those wound tube or pleated filters)?

Thanks;

Josh