I use Matrix in my 2 HOBs on my largest tank. As I track my nitrates week by week (ammonia and nitrites are always zero), I have seen a slow, but steady decline in nitrates. I've removed the bio-wheels from the HOBs, and keep floss in there for the big poop that I rinse in tank water during changes.
Purigen is a God-send. I use it in my largest FW
tank as well as my SW
tank. Good stuff, and since it can be regenerated, a helluva lot cheaper than other products out there.