I have been running two bio-reactors to help control nitrates in my 90g for over a year. One is filled with Seachem Matrix, and the other with Seachem Pond Matrix. When measuring the nitrate level coming out of either of the reactors I see no nitrate reduction over that of the tank water. I have varied the flow, and insured that the water through the reactors is far removed from the oxygenated inflows from the filters. My conclusion is that these bio-reactors are doing little to nothing in nitrate reduction. Have any of you found that bio-reactors work to remove nitrates to any significant degree?