so i'm building a 240G plywood tank, and i'm in the planning stage of filtration. what i'm thinking is using a 50G rubbermaid tub that will overflow into a 20G wet/dry filter. the 50G tub will be full of bio media. and the reason for the 20G is i've got two just laying around. i'll be running a 1800 GPH pump. so what can i improve on?