What Media For A Canister Filter?

[Aulonochromis]

I have a canister filter and I'm wondering what I should run in it. Should I just fill it with live rock?

 

[AMS]

Unless you want a nitrate factory you should fill it with LR. Ideally you should have at least 1 pound of LR per 1 gallon of water, so you need to have LR in the actual aquarium as the canister wont hold the amount of LR needed.