I thought I'd comment on the label "nitrate factories". A biowheel certainly doesn't cause more nitrates to be produced in a tank. It does, however, cause higher levels of nitrates to be released into the water column. This is because the conversion of nitrite to nitrate occurs in the absence of any area where denitrification takes place. In order for nitrate produced by bacteria on the biowheel to be converted to nitrogen gas in anaerobic areas of the sandbed or live rock, it must travel through the water column to get there. Here, it can be utilized by nuisance algae, corals, clams, etc. Usually, though, it is much more efficiently utilized by algae.
In the absence of a biowheel, the mineralization of proteins, other organics, etc. to nitrate occurs in close proximity (on the surface of LR, in the upper layers of the SB) to anaerobic areas where it can then be reduced to nitrogen gas without traveling through the water column to get there.
This is not to say a tank with a biowheel could not have a reading of zero nitrates when its water is tested. Actually, we have a newly set up tank here on campus with an incredible outbreak of Valonia nuisance algae. The water tests at zero nitrates because any nitrates produced are quickly consumed by the algae.