Think I Figured It Out

[Goes to 11!]

I'll set it up and work on cycling it normally. Do I have to add fiber or cloth pads in the filter, or will pillow stuffing suffice? Or could I take a large cartridge for my whisper filter and cut it to fit in the eheim? Would that work?

I am assuming you meant in addition to the required biomedia, Does it not have a pair of course blue sponges [for mech]? IME filter floss clogs far too quickly to be very effective in canisters.

You can easily find the blue sponge pads on amazon.