The number for fbf looks way too low to me, perhaps they are referring to the old gravel style fbfs. The enormous surface area of the sand in the the fbf (just under 8000sqft per cubic foot) should allow a much smaller foot print and according to this site they can chew through up to 100% of the ammonia in a single pass. I realize this is a manufacturer's site but I have read about high conversion rates other places as well.
It could also be that they are referring to the cost of running the filter, as RBC can run with only a small air pump and a sand fbf requires water to be pumped into the sand at good rate to keep it all moving.
I am not knocking on RBCs at all but, I have just read alot of material that backs sand filters. I am really interested in reading that report, but the link isnt working. Could you fix the link?
