LOL!
i love this debate.
the argument for bio-wheels goes something like this..
1. water has about 7ppm oxygen available ....
2. air has something like 30,000 ppm oxygen available...
the bio-wheel allows oxygen to be obtained from the air for the establishment of nitrifying bacteria.
i TOTALLY agree with this, and think that the bio-wheel filters are great.
i DISAGREE that bio-wheels are the "end-all" and that they can outperform canisters or even aquaclears for that matter.
2 sponges in an aquaclear (even at 7ppm Oxygen) will have TONS of bacteria colonies due to the large amount of surface area for attachment.
the bio-wheels have much, much less surface area for attachment-- even if they draw oxygen from the air.
most people i have talked to notice NO difference in the biological filtering capacity from an aquaclear, an eheim, an emperor, etc. i myself have had extremely stable biological filtration with no bio-wheel filters at all.
the reason i run an emperor 400 and a 280 on my tank??
i think that they DO work well, and i think that the actually craftsmanship of the emperors is a bit better than other power filters. that is it....nothing more.
i would take an eheim over any of them, any day of the week though.
M