Deniballs are made from a special biologically based plastic material and are designed to provide a long-term carbon and food source for anaerobic bacteria within our Nitratereductors. In the absence of oxygen, these anaerobic bacteria metabolize the Deniball material to accelerate the reduction of nitrates into nitrogen gas. One box of Deniballs (0.2 gallons) for the Nitratereductor 400 and 3 boxes for the Nitratereductor 1000 is enough to be the sole source of supplemental food within the reductor for 12 months. For the Nitratereductor 5000 you will require about 1.2 gallons, about 6 boxes or one bucket, every year. Changing the Deniballs every 12 months is recommended to ensure safe and maintenance free denitrification for your fresh or saltwater aquarium.