This is one of those things where everyone has their own theory or preferences.
I'll just throw this in, but it's not the only way, I've done power filters a variety of ways over the years. I absolutely agree with the economy of ditching prepackaged cartridges in favor of customizing media. My current preference is some permanent bio media along with poly fiber. People debate bio media-- type, pore size, etc. I prefer
Seachem or
Eheim. For poly fill I just get a simple
poly filled pillow, a lot more economical than specially packaged "Aquarium" poly fluff.
In a power filter I run something like 1/3 bio media, 2/3 poly. I typically change 1/2 or 1/3 of the poly fluff at a time based on visual inspection, stocking level, etc. You can also rinse poly out fairly easily, based on that I've run poly only filters at times-- my water is well water, so as long as temperature is moderate rinsing doesn't hurt beneficial bacteria. That's it. That's my list for power filters. I've done it for years.
I do something essentially similar in canisters, aside from using any coarse sponge or flow enhancing mechanical media that comes with the canister.
