I'm in the process of setting up a new 75 gallon tank and will be using a canister filter. This will be my first cannister filter and I'm not sure what to add as media. I have 3 trays and plan to use some of the white ceramic ring looking things (not sure what they are called) and lava rock. That gives me 1 tray left, I'd like something that will be more on the mechanical filter side of things for water clarity since the lava rock and ceramic rings are handlining the biological side. Am I on the right track?