Mechanical media at the bottom and bio media at the top is how I do it. On my Sunsun 302 I run several layers of sponge in the bottom tray, plastic pot scrubbers in the middle and various bio media in the top (302 is only a 3-tray).
On my Marineland C360, layers of sponge in the bottom two trays and bio media in the top two.
I don't run any type of chemical media like carbon or purigen, but if you wanted to run those, they go up top as well.
On my Marineland C360, layers of sponge in the bottom two trays and bio media in the top two.
I don't run any type of chemical media like carbon or purigen, but if you wanted to run those, they go up top as well.