How does biological aquarium filtration with sera siporax work?

New sera explanation video


Biological aquarium filtration is a complex process essential for clean, healthy water. The new sera video "sera siporax - biological aquarium filtration" explains how biological filtration takes place: Purification bacteria in the filter make sure that pollutants such as fish waste are being broken down biologically. They require a filter medium on and in which they can settle to fulfill their task. However, the filter medium must meet some criteria to make it optimally suitable for being settled by purification bacteria. This video clearly shows which criteria they are and how you can check whether these criteria are being fulfilled by a filter medium.

The optimal surface structure

The filter medium must provide a certain surface structure as to allow purification bacteria settling on and in a filter medium. The bigger the surface, the smaller the pores. Above a surface of approximately 450 m² per liter, the pores are so small that no bacteria can grow in them anymore. As proven in a university study, 270 m² / l is the optimal settling area, since the pore size then exactly corresponds to the size of the bacteria and the bacteria thus can settle ideally. sera siporax provides exactly this surface.

sera siporax is made from a mixture of recycled glass powder and salt crystals of an exactly defined size. The size of the salt crystals exactly corresponds to the the size of the bacteria – that is particularly important since thy define the pore sizes as placeholders. The mixture is pressed in ring shape and sintered, that means burned,  at approximately 780 °C (1436 °F). The rings are then washed out, removing the salt crystals and leaving the pore structure behind.

Quality criterion No. 1: Porosity

The porosity described above is the first quality criterion that characterizes a good filter medium. This property is very easy to check: in case of sera siporax, cover the ring with a finger and blow through it. Due to the open pore structure, the air passes through the outer walls of sera siporax. On the contrary, ceramic rings, for instance, have closed pores that do not allow air to pass through the wall.

Quality criterion No. 2: Connectivity

Connectivity is the second quality criterion. Under a microscope it can be seen that sera siporax has an open pore structure and that the pores are connected among each other. In comparison, ceramic, for instance, has many pores, which however are not connected among each other. Sphere shaped filter media have very fine pores, but they have the disadvantage that they do not allow for water flow. They can therefore not be settled inside. Furthermore, the pores are too small to allow for an optimal settling area for bacteria.

The absorption test shows that the interconnected pore structure of siporax absorbs the liquid much quicker than, for instance, ceramic. A similar test with a highly viscous liquid proves that the liquid – and correspondingly also the bacteria – can enter up to the inner ring wall only in case of sera siporax. Filter media made of ceramic and sphere shaped filter media, on the other hand, are only being settled at the surface.

sera siporax for biological aquarium filtration

The combination of both properties – high porosity and high connectivity – makes the high filter performance of sera siporax possible. Self purification is another characteristic: should bacteria die due to a reduced nutrient supply, they are being broken down without any residue by the bacteria themselves. Sludge deposits may cover the pores, which inhibits the water flow. An effective prefiltration, e.g. with the sera UVC-Xtreme, prevents this.

Removing algae and conditioning water with sera siporax

sera siporax is available in different varieties:


There are two additional versions of siporax that also fulfill further functions besides biological aquarium filtration. The carrier medium siporax is enriched with 80 different bacteria strains taking up their useful work upon contact with water in sera siporax bio active Professional as well as in sera siporax algovec Professional. In case of sera siporax bio active Professional, pollutants such as ammonium and nitrate are removed from the water, preventing water pollution. It is therefore also called a “dry water conditioner“. sera siporax algovec Professional controls algae: the nutrient utilizing bacteria in particular remove phosphate from the water, which is a main nutrient for algae. Algae growth is inhibited and existing algae are lastingly reduced due to the principle of nutrient competition – entirely without using chemical agents.

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