Bio Ball provides a large surface area on which water-filtering microbes can grow. They are typically used in fish tanks and fish pond filters to transform potentially harmful ammonia into benign nitrates. You can use it in marine and freshwater aquarium filtration. Most new aquariums take 3-6 weeks to fully cycle, meaning that the nitrogen cycle can successfully process ammonia into nitrates. Place the bio balls in the stream of water running through your fish tank's filter. Although bio balls will catch some pieces of algae, they are not meant to be used as a physical filter. Installing them downstream of a filter membrane will help keep them from clogging.