The midwest aquatic bio denitreator is a reactor with sulfur and calcium reactor media thats serves as a breading ground for anerarobic bacteria that in turn eats up ones nitrates to put in simple non boring terms. Its easy to set up easy to cycle and has not been any trouble. and it works! Its not a matter if a tank crashes its a matter of when one will crash. For example several of reef centrals tanks of the month have crashed due to tempature controle breakdowns, kalk ca reactor accidents and nitrates. the unit was pricy one for my sized system retailed for around 500 bucks. I would rate the unit an B...since my nitrates arnt a problem I have not pushed the unit to its full potental.