Deni Balls .8 liter, Aqua Medic. Filter material and bacterium food for the Nitratereductor. Deniballs are made of a special biologically produced plastic material. In the absence of oxygen, anaerobic metabolize this material. The bacteria are used for the reduction of nitrates, thus reducing nitrate to nitrogen gas. One to three Pyamid packages (of 0.8 liters each) is enough to supply the Nitratereductor as the sole food source for 12 months. For the Nitratereductor 5000, about 5 liters (1.25 gallons) are required. Changing the Deniballs after approximately 12 months is recommended to ensure safe and maintenance free denitrification in fresh and salt water aquariums.