manuelink, I have to agree with gt3000xx; mechanical filtration, properly employed, can be highly beneficial. On my heavily-fed mixed reef system, I religiously use a mixture of pre-fab and DIY filter socks - On my weekly replacement schedule, I have never had the slightest issue with nitrates with any of my tanks since the tank was completed cycling. It even goes for 2 weeks at times. The "nitrate factory" thing has been so over-hyped IMO that is has become urban legend. I believe that there are elements of truth to it, and does become a valid occurrence if the filtration media (regardless of whether the media is filter socks, foam, floss, etc) is not cleaned or replaced on a suitable schedule.