Bio chem stars are a biological filter media providing an ideal home for beneficial bacteria to coloniser these bacteria are constantly breaking down harmful ammonia produced by the fish into less harmful toxins such as nitrater renas nitrazorb pouch will then remove this levelr this media is renas most efficient media for biological filtrationone pouch contains roughly 20 stars the stars have four times more bacteria capacity than standard ceramic mediar use one star per 20 litres 5 ga