I have a couple of Penguin minis - nice filters. The biowheel is supposed to provide a huge amount of surface area for good bacteria to grow. It's also partially exposed to air, so those bacteria get plenty of O2
You're not supposed to ever clean the biowheel, even if it's surface becomes gunky. Sometimes mineral deposits will grow around the axel and prevent it from spinning, and you can remove these with a damp paper towel.
Once a week at every gravel vac/PWC
, I pull out the cartridge and rinse it off. I used to do this in a bucket of tank water, but I've grown lazy and now do it under tap water. I can do this for about 3 months until the blue fiber pad wears thin - only then do I replace the cartridge.
I don't worry about the carbon in the cartridge, although I would remove it if I had been treating the water with meds. If you want to run carbon all the time, you could cut the back of the cartridge with an exacto knife, remove the carbon every two weeks, and replace it with fresh carbon.
My only complaint about the Penguin Mini is the propensity for its impeller to get gunked up. When I notice the output decreasing, I know that it's time to disassemble the filter and clean the impeller, the two bushings, and the wells in which they sit.