PURE Aquarium is a bacterial treatment for aquariums of all sizes. Inside every ball there are millions of live bacteria and enzymes. Once added to your aquarium, the bacteria and enzymes inside each ball will start to break down the ammonia and nitrite in your aquarium's water. PURE Aquarium also breaks down organic waste, which is often the cause of poor water clarity. Using PURE Aquarium on a regular basis reduces the amount of filter cleaning and maintenance. Each pack contains 50 balls. Simply add 1-2 balls for every 25 litres once a week. Add the balls into your aquarium filter or directly into your aquarium. We recommend the use of a filter bag to contain the PURE Aquarium balls. If using PURE Aquarium for the first time or if your aquarium has clarity problems, add 5 to 10 balls per 100 litres of water. PURE Aquarium is designed to improve water clarity and quality when it is affected by organic waste, not algae related issues that cause green water.