I have a 90g all-glass aquarium and I have 2 Emperor 400's on it. I went with the initial carbon filters that came with them, and have just recently began a process where I am taking one of the 2 out, and replacing it with 2 in that slot (as they have 2 slots) with the "E" sized carbon filters. The word is that this will really polish the tank, and obviously retain a great deal of that good bacteria that you are wanting for stability.
