here is a video of the filter working... please watch it until the end.... last time i did a 50% change was 2 weeks a go and the last time before that was like a month! look how clean the water/filter stays...
i like the double filter cartridge; because the 1st retains most of the junk and then the second one cleans the water again, then the bio-wheel does the rest... note that my bio-wheel for some reason is bent a bit =) i think i dropped it way too many times... but still...it works.
also you can wash the cartridges every 2-3weeks and reuse them for like ...tsi months... if you always clean it...
i got this:

does the job! and helps me remember when i have to do things- paid $10 on ebay!!!
enjoy the video:
[youtube]http://www.youtube.com/watch?v=V4Pw1fUdQ6s[/youtube]