sera siporax pond is a fully biological filter material for almost all garden pond filters.1 liter (1 US quart) sera siporax pond provides as much settling area for bacteria as approximately 34 liters (9 US gal.) of clay filter material. Prefilter with sera biofibres coarse to prevent large particles from entering the biofilter.sera siporax pond provides bacteria an extremely large amount of open-pored tunnel structures. This allows an ideal supply of the bacteria with nutrients and a smallest amount of fresh water. There are oxygen-poor conditions within the tunnels. This makes the bacteria crack nitrate to get enough oxygen. Consequently they continuously break down nitrate and the pond water remains low in nitrate.The surface of one liter (one US quart) of sera siporax Professional has almost as much biological breakdown power as 34 liters (9 US gal.) of clay filter material.Calculation formula for sera siporax pond:One single liter (one US quart) sera siporax pond is sufficient for purification of 1000 liters (264 US gal.) pond water with 20 pond fish of 10 cm (4 in.) length each or a comparable stock [representing approx. 1.5 kg (3.3 lb.) of fish fed with up to 40 g (1.4 oz.) high quality food per day] and release it from organic pollutions in long terms.