Aquatic Life Polishing pads work great
Not sure if you have C3 or C4 (typo??) or both. I have both. The mechanical media holder on a C3 is about 1/2" thick and the C4 is about 5/8."
I use Acurel debris reducing pads cut to fit and AquaticLife non-woven filter pads for micron particles. It comes in sheets of 300, 100, and 50 micron and I have all three types. Here is what it looks like if you click throught the filtration section of my photobucket account and read the subtitles.
HOB Filtration Photos by Paul1792 | Photobucket
My water is so crystal clear and polished, it looks like I'm running a canister filter and a UV sterilizer. Also, I use seachem purigen in the chemical chamber of all my fluval C's. [Oh ..... and looking at my filters ... aren't you glad you don't have that messy AquaClear media basket.
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Note 1: Be careful .... Hagen really wants to make sure you use their pads so they made the mechanical media holder odd shaped ... a bit taller on top than on the bottom rather than a perfect rectangle or square so you should use a template when cutting or put an actual pad on top of the sheets of media when you cut it. I have run a factory pad together with the 50 micron pad after the factory poly-fiber and the 50 micron pad gets caked with dirt anc cloggs before the factory pad gets full.
The aquaticlife pads are only 1/12" thick so you can run a C3 with either one or two layers (ie 100 micron + 50 micron) ..... and a C4 with either two or three layers of the pad (ie 300 + 100 + 50.
When using the 100 or 50 micron pads, be certain to put the "felt like side" first or they clog very quickly.
The pads are hard to find at retail stores (at least in Pensacola FL) so I buy it on line. Petco has all three sizes at reasonable prices:
Aquatic Life Filter Media Non-Woven Pad at PETCO
Good luck.