This is a very useful thread I have a Eheim 2217 canister for a 50 gallon aquarium. Presently, I have 35 fishes in there (this is the current staff): one Discus, Gymnocorymbus ternetzi (black tetras) (4), Paracheirodon innesi (neon tetra) (8), Hyphessobrycon megalopterus (phantom tetra) (6), kryptopterus (8), Rasbora heteromorpha (3), Rasbora espei (1), Pangio kuhlii (2), Botia kubotai (3) and Xiphophorus maculatus (2). I also have a few species of shrimps: Atyopsis moluccensis (3) and Neocaridina heteropoda (yellow shrimp) (4). I have to do two 40% water change every two weeks.
Post 5 from momotaro is very complete, but the other commentaries from the members are also useful. I read this post about eight months after the implementation of my aquarium. At that time there were signs of eutrophisation.
As my 2217 is superior to the volume of my aquarium, I am only at my second cleanup of the media, which means once every 8 or 9 months. Contrarily to what is proposed in this thread, I never got rid of the small balls and did not boiled them, I just rinse three times and agitate 2/3 of them with the aquarium water, whereas I treat all of the cylindric media. I do not want to disturb the bacteria equilibrium too often. This is why I take care of the small balls.
Although I imagine that cleaning regularly the filter is good to remove nitrogen in organic form of bacteria and various debris (and probably other chemical elements are also removed)
At some point I had some difficulty in restarting the filter. Pulling down the smaller or exit tube of the canister so that it flowed into a bowl on the floor, instead of having to fight for gravity to push the water two feet higher gave a really good pressure. Once primed this way the propeller would easyly push the water in the aquarium once the exit tubulure was replugged.