Canister filter stages question.

[exodon king]

the bio balls should not be "dirty" unless you have them as the first thatge of filtration (which is not a good idea).

generally in a canister, you would want to go with a more dense media, so you can actually fill each compartment properly.
the best bet is something like bio-max pellets. alternatively there is substrat-pro and matrix.
if you are not willing to spend the money on a good bio-media, you can always just go with ceramic (or glass) rings, availible at your LFS.