I added a fluval 307 and a hydor nano skimmer to mine in the first chamber, filled the second chamber with cheato.
Works well for me. Dont think of the canister filter as a filter but more of an area to house more biological media or if you need it a chemipure or other carbon sock.
I just filled mine with all bio rings (of your favorite choice) and remember to rinse weekly (or monthly depend im ng on your tank) so nitrates dont build up. Use to water if you can. And NO rinsing in fresh RO water wont kill the bacteria. Brandon429 has many threads on that here on this site
Look at updating light as well...that's when I noticed the biggest change to my biocube 32...when I added proper lighting!