Filter reactors are used in marine aquaristics as well as in freshwater aquaristics for a wide variety of purposes. For example, they can be easily used as a filter with appropriate filter materials such as filter carbon or ceramic rings as a biological filter to optimise the filter performance of an aquarium. They are also often used as problem solvers, in which certain adsorbers, such as phosphate or nitrate adsorbers, are used in the reactors in order to get algae problems caused by an excessive load in the aquarium under control. Especially when adsorbent filter materials are used, their efficiency is clearly superior to conventional filter types, as they can be used in a more versatile and targeted manner. For the easiest installation, the reactors should be able to be used either directly in the aquarium or, alternatively, in the filter sump for larger aquaria. The reactors are operated either via a small feed pump or via a bypass of the main feed pump of the aquarium. The flow rate of the reactor should always depend on the filter material or adsorber used.