While going through some of the fish websites in search of the cheapest quote for my new tank i came across some filters which claim to only remove nitrate,apperently they work by starving anerobic (excuse spelling) bacteria of oxygen so that they have to strip it from the NO3 converting it into nitrogen gas (or something like that?).However they weren't cheap and i have wasted so much money on products claiming to do this that i am a little cautious to part with my cash,has anyone else heard of these filters or even better used one and if so do they work?