I'm surprised this article hasn't generated more conversation yet...
http://www.advancedaquarist.com/2005/6/aafeature
"In terms of processing nitrogenous wastes from aquarium inhabitants (specifically ammonia, nitrite and nitrate), none of the experimental treatments (plenum vs. sandbed; deep vs shallow; coarse vs. fine) appeared to have a significant advantage."
"The significant differences among the experimental treatments were almost entirely in the buffering capacity of the sediments rather than the biological breakdown of nitrogenous waste products."
"Our experiment shows no evidence for any of the espoused benefits of a plenum..."
http://www.advancedaquarist.com/2005/6/aafeature
"In terms of processing nitrogenous wastes from aquarium inhabitants (specifically ammonia, nitrite and nitrate), none of the experimental treatments (plenum vs. sandbed; deep vs shallow; coarse vs. fine) appeared to have a significant advantage."
"The significant differences among the experimental treatments were almost entirely in the buffering capacity of the sediments rather than the biological breakdown of nitrogenous waste products."
"Our experiment shows no evidence for any of the espoused benefits of a plenum..."