I'm not a very chim person but this is what I do and believe.
Heavy mechincal filtration (thick layer of wool) before hitting the biological filter media in filter system. Flowrate can be fast but one must remember that the wool may choke and water can't pass through them as good as they are new.
But if flowrate is high and filter wool is not doing the mechincal filtration well enough, dirt will start pushing through and they will all start to choke the media underneath. Fast flowrate work well if the surface of the mechincal filtration is huge. If small chances of clogging is higher.
Just the way I keeping my fishes.
