Deniballs – 25 ltr. is a filter material and bacteria feed for our Nitratereductor. Deniballs are manufactured from a unique biologically based plastic. One to three packages of 0.8 liters (c. 0.2 gal) each is enough to supply the Nitratreductor as the sole food source for 12 months. For the Nitratreductor NR 5000, about 1.3 gal. is required. Changing the deniballs after approximately 12 months is recommended to ensure safe and maintenance free denitrification in fresh and salt water aquaria.