You could really go either way in the filter you're using. It's a piece of cake to clean MarinePure when it gets gunked up. Easier than cleaning the filter pad lol. The only time you really need to make sure that you have a serious mechanical prefilter is when it's a PITA to rinse the MarinePure.
Got it, thanks Clay. I'll see what it looks like next time I open the canister. I really hate having floss and the like in canisters as that increases maintenance and the water's crystal clear as it is with just the sponge/Purigen. I would have expected it to be even less demanding of a very fine prefilter than ehfisubstrate, bio-chem beads (remember those?) and the like, actually, due to the open pore structure.