ISTA 50pcs BIO BALL (S) 31.5mm Blue Color - Aquarium Filter media Pond balls Helps in distributing smooth water flow through the filter. Compact in size to fit small filter or any other filtration system. Works with both marine and freshwater tank. Leads the water flow through a longer traveling distance within the Compact Bio Ball to more effectively decompose toxic ammonia and nitrite through biological filtration. Leads consistent and steady water flow to achieve best purifying results. Non-clogging so intensive cleaning is not necessary. This prevents washing away nitrobacteria colony. Numerous chambers inside the bio-cube provide optimal oxygen dissolution. Distributes smooth water flow through the filter. Provides an excellent biological filtration ability to assure the best water quality. ISTA 50pcs BIO-BALL S ( 31.5mm ) Blue Color #I-291