Tetra Pond 16783 1200 Gallon ClearChoice Biofilter Easy out-of-pond accessibility and simple maintenance. Mechanical pre-filter sponges-remove suspended debris to improve water clarity. Bio ring media provide massive surface areas for beneficial aerobic bacteria to adhere to and multiply. Tetrapond internal spray systems and trickle flow technology disperses pond water slowly and evenly through the bio rings. 1.25 drain fitting.