I'm new to canister filters. Got a used Fluval 306 for the new 75-gal that I'm setting up and really like it so far. My question is, what media do you use in the stackable trays? Right now I have the "stock" setup with foam on the bottom, fluval's ceramic bio media in the middle, and carbon in the top. I was thinking of swapping out the carbon with another set of bio media. Pros/cons? I never used carbon in my old 90-gal tank, which had a sump, so I am wondering if I'd be better off packing as much biological filtration as possible. This tank will be housing severums tetras, and a convict.