Media type, media volume and turnover are all important factors to good filtration, but each one needs to be considered independently. Each one does have an effect on the other, but each one also holds it’s independent responsibility.
　
Water Flow - You need to have enough water movement to move the waste into the filters intakes… or you need to accept you have ineffective mechanical filtration and therefore take on the responsibility of manually cleaning the tank regularly (and experience the consequences when life gets busy and you don’t have time).
　
Media Type - Mechanical media is for filtering out particles and bio media is for housing bacteria. The value of bio media lives in it’s porous nature. So you want to thoroughly remove particles from the water or else those particles will clog the pores making bio media drastically less efficient.
　
Media volume - In my opinion/experience this is the least important factor being discussed here. If you have a dozen foam blocks in a row that are all the same density, the first one will catch the vast majority of the waste and slow down the flow rate while the others just sit there. Therefore it helps to progressively increase the density of the filter media (example - open cell sponge first, light sponge second, dense/fine sponge third, quilt batting last).
　
Regarding bio media, your tank will need X amount of bacteria. If you have enough surface area to house 10X bacteria, your system will still only house X bacteria. To create an example… if a couple has 4 kids, they ‘need’ a car that can seat 6. Buying a bus that seats 60 doesn’t make your family any larger. It just means they have a lot of empty seats.
　
Also remember that bacteria can and will live/grow on any surface, not just bio media.
