Originally Posted by DragonForce
You don't really need biological filtration if you're using substrate and live rock.
Just to clear that up, Live rock and Live sand ARE biological filtration. They are much more efficient at the filtration and much more thurough in that they process nitrate and live little of it behind (in a balanced system). As hara pointed out, UGFs have a tendency to trap waste material where it can't be cleaned up by the natural processes (both bacteria and critters) which results in higher nitrates.
In todays "natural" approach to SW
aquariums you'll notice it's MUCH easier and MUCH cheaper to run a successful reef
system. In the 70's and 80's you had a lot of SW
tanks that were FO
... they had to be that way because nitrates were high with the typical filtration systems (wet/dry and ugf
were the main approaches). Fish can tolerate nitrates ok, but any invert will not do well in a system with high nitrates.