I recently just set these two filters up on a 75 gallon (the tank is still cycling and has no inhabitants besides a few plants), and was wondering how often I need to clean them. The Emperor 400 instructions say to clean the impeller, spray bar, and intake tube every month, and to replace the filter cartridge every 2-4 weeks. I was wondering how often I need to replace the carbon in the filter and if I should alternate replacing the two inserts or replace both at once? The AquaClear instructions say every 3 months to clean the motor. It also says to clean out the case and intake tube but doesn't tell me how often to do it. I would like to know how often to clean out the case and how often I need to replace the filter media. THANKS!