THis type of de nitrater filter can and does work but they are very problematic. Very regular testing of the water comming out of the de nitrator must be done to insure it is working properly. Idealy you would want a very low but not anarobic condition inside the denitrater. If it goes anarobic from to slow of a water flow, it is not uncommon it will put hydregen sulphide into your aquarium water which can wipe out your tank. If water flows a little to fast thru the denitrator it can be adding nitrites into the aquarium water. A very high quality water flow controll valve is a must on these. It is also very important that the water flowing thru the system is prefiltered real well, mostly to prevent debris from cloging the controll valve. Many people use a glucose solution to feed the bacteria inside the denitrator, that can be tricky to know how much to add in relationship to flow rate and actual nitrates needing to be processed.
They can work but they are diffacult to get to work properly and if you make a mistake it can kill all your fish. They were real common about 12 or 15 years ago but were so problematic that they have for the most part dissapeared from the hobby.
Wasn't aware drawbacks so fatal...thanks
Water changes work better, are safer and free!!!!!
Joel