The (very few) commercial de-nitrators I've seen people post about have either been drastically less effective than the DIY version or insanely expensive. There's plenty of info here: http://www.monsterfishkeepers.com/forums/showthread.php?t=180385 I cant find the link, but some Scandinavian company has an effective freshwater protein skimmer. Its aimed at large-scale Koi ponds, but they may have a smaller one. Do some searching homie.