Yea there was an interesting paper (which i cannot find) that researched different media for effective bio filtration and sponge 20ppi and 30ppi were extremely effective far more effective than all commonly available bio-balls. The only thing that was significantly better than sponge was k1 media in an mbr (sorry adding it to your canister filter isn't going to do much good).
For my classic 2215, I swapped out all the ehiem bio media for blue coarse sponge disks. It's got like 7 of them stacked bottom to top. To me it's simpler that way and easier to clean. My penn plax 1500 is just coarse sponge in each tray as well.
I always pre-fill my canisters with water before I snap the tops back on. I fill them to the point water wants to squirt out when putting the top on. They take right off for me this way.