denitrator concept

Have a 125 reef tank and a 35 gallon refugium. Refugium pours into the tank via gravity and I have some spare room I'd look to put to use. I'd like to use a 5' tall piece of 3" or 4" sch. 40 pipe and fill it with 4" of reef sand. I would bypass a trickle flow off of the refugium feed, to the...