Nature s Ocean® Bio-Activ Live Gravel™ has natural live substrate which instantly cycles your aquarium. This gravel is perfect for all freshwater fish and contains live denitrifying bacteria & trace elements. To set up a new tank empty contents into aquarium & fill with dechlorinated or distilled water. ActivFlora™ will separate into 2 layers & finer grade substrate will settle on bottom layer. Add slowly when supplementing existing system & lower tank level beforehand. Grain sizes range from 0.1-4.7mm across the 8 varieties.