feel free to move this if it's in the wrong place.
http://reefkeeping.com/issues/2004-05/r ... /index.htm
http://reefkeeping.com/issues/2004-05/r ... /index.htm
The only motive force sufficient to move enough water through the rock, so that it may act as an efficient denitrating site, is the force generated by the animals, mostly the worms, living in their burrows