I am setting up a 120 with 40 gal sump. What I am doing is putting 2 layers or 1/4 inch thick egg crate from Home Depot (misnomer, this is the stuff they put in drop ceilings where the lights are). I put about 3 liters of denitrate in the little cubes. Flow should be low as 3 of 4 sides are covered so theoretically I should create locally anoxic conditions. Will see if this does anything as I am setting up 2 and the second sump will have the egg crates in case it works but empty in case it does nothing. Will give it about 6 weeks and see if nitrates vary. If no effects will have room in the sump to add some BCBs and see if that helps. Kind of wonder if this is a waste as I will lose the best indicator for when to do water changes..........