Simply add 2 balls per 25 litres of water once a week directly into your aquarium filter to maintain clear & healthy water. Maintains crystal clear & healthy water. Pure Aquarium is a bacterial treatment that helps to maintain crystal clear, healthy water in freshwater aquariums. Inside every ball there are millions of live bacteria and enzymes. Once added to your aquarium filter, the bacteria and enzymes inside each ball will start to break down ammonia and nitrite. This will also work to clean up organic waste, in turn reducing filter maintenance. Pure Aquarium is safe for all freshwater fish and invertibrates. Add the balls into your filter for best results. We always recommend the addition of oxygen into your tank using an air pump or venturi. Pure Aquarium will not prevent algae growth.