I am looking at adding some Seachem Matrix to the two Canister filters (both Aquatop CF500UV) on my 120G tank. I have heard mixed reviews on it's effect on reducing nitrates. Does anyone have an opinion on it's ability to reduce nitrates in a canister filter? Also any thoughts about Matrix in general? I would also welcome input on how much to add. My tank is fairly heavily stocked and nitrates usually run about 40-50 with weekly water changes of between 40-50%.