Do you have adequate amounts of Live Rock and Live Sand in your tank...?
OK then, a goodly amount should be able to supply you with all the "Biological Surface area" needed to maintain a healthy and tank stabilizing population of nitrifying bacteria...With that and the Oxygenating flow and the Skimmer, you should have a pretty decent handle on your tanks overall filtration needs...
Bout the only things lacking (for want of a better term) are "Mechanical" (actual physical trapping and removal of parts pieces and chunks, both organic and inorganic) and "Chemical" (molecular and ionic absorption of "compounds" both organic and inorganic) and some form of "Denitrification"...
A canister can help with the first two, but not much help at all on the third, and can even be a liability if not maintained properly...
"Mechanical" the sponges (both course and fine) will trap suspended deitrus, algae, organics, food particles, sand and all the other "floaters" in the water column and help keep the tank looking clean, clear and not "dusty" in the water...
Removing them (organics) before they decompose and add to nitrate build up will help with overall water quality, but the trick is to be sure they are "removed" before they decompose and produce 'trates...
This entails regular "weekly" if not bi-weekly pulling and rinsing and squeezing...Now we already established that you had plenty of surface area for bacteria, so it's not a problem to pull the sponges and rinse them in hot running water squeezing and cleaning well..there will be no noticeable effect on the bacteria populations...IF you do this often enough to keep them from becoming established in the first place...OFTEN is the key...
Chemically, the canisters offer a contained flow pattern which can work to your benefit "suspension-wise" for running Carbon and or Phosphate removal medias...
You'll get more benefit from your medias if you have water flowing over (and thru) a greater portion of the surface area than having a bag sitting in the corner of your sump...
Carbon looses it's effectiveness rather quickly...(24-48 hrs maybe a little longer if you use larger quantities)..But that's not a problem cause your gonna be in there every week anyway changing and cleaning the sponges, so just toss a fine mesh bag filled with carbon in once a month or so to "polish the water, and then pull and dispose until next time...
Phosphate removers last a bit longer, but will need to be "fluffed" in their bags from time to time to expose the most "new" surface area to the running water...(again weekly pull/fluff/and replace)...
Both of these medias will loose their effectiveness rapidly if "clogged" with fine particles so running the course sponge first then a media bag and then the fine sponge or better yet a handful of "Poly Filter floss" (which really traps the fine particles and can be thrown away rather than "cleaned") before water returns to the tank (catching loose carbon and/or phos media) would be the preferred way to set up your canister...
So...No "balls, or rings, or stars or bio media" is needed...Sponges and floss catches debris, but need to be cleaned OFTEN...and chemical medias will need to be fluffed and kept in suspension to work to their best effectiveness...