HIGH-EFFICIENCY BIOLOGICAL FILTER MEDIUM: Maximizes pond clarity & nitrification with unique tunnel structure design for optimal bacteria nutrient absorption. NITRATE REDUCTION FOR HEALTHY PONDS: Advanced oxygen-poor tunnels inside encourage bacteria to reduce nitrate, keeping pond water low in nitrate. MAINTENANCE-FREE & LONG-LASTING: Designed for all garden pond filters, this 50L pack effectively cleans up to 50,000L of water with 1000 fish (each 4 inch), minimizing maintenance efforts. OPTIMAL BACTERIA HABITAT: Offers bacteria vast open-pore tunnel structures for superior water and nutrient flow, significantly outperforming traditional filter materials. EASY SETUP WITH PRE-FILTER OPTION: Use with sera biofibres for enhanced performance, preventing coarse pollutants and extending the life of the siporax pond filter medium.