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    Disinfecting a filter

    A guide to cleaning

    Who doesn’t know it: You have bought a used external filter or would like to use a filter in another aquarium. To prevent the transmittal of germs and especially algae spores (such as the pesky Cladophora sp.), disinfecting the filter is recommended.

    To clean a used filter you can fall back on various options. Vinegar or chlorine cleaners look like an option because of their strong disinfecting effect, but they can cause the rubber seals and hoses to lose their plasticizers and make them harden. Repeated use of these agents can therefore lead to leaks. For this purpose, commercial citric acid for descaling coffee machines is a much better option than vinegar or chlorine cleaner, which in addition to their property as a limescale remover also acts slightly antiseptic.

    First, the filter, including baskets and filter media is roughly cleaned. All inner parts need to be rinsed under running water. Very fine and dirty filter media (like fleece) should better be removed and replaced.

    washing filter spomge

    If technically possible, a general cleaning would also be a good opportunity to remove, disassemble and clean the impeller from the filter head. Subsequently, all components are reassembled, the filter is filled with fresh water, closed and the hoses are connected again. The ends of the hoses for the filter inlet and the filter outlet are now being lowered into a bucket, which was positioned next to the external filter beforehand.

    filter and bucket

    Inline technology such as an external heater or an inline diffuser - if present - can stay connected to the hose line, if those elements are in need of cleaning (it is advisable to do it anyway). To keep water from leaking, the CO2 tube line of the inline diffuser should be either plugged shut or secured with a check valve. The bucket is filled with sufficient water, closing the filter circuit, and the external filter can now be connected to the mains. The hose end of the filter suction side should always be under water. If necessary, this end of the filter hose is weighted with a stone, for example, so that it really can not raise. The filter should run without problems. For the next step it is important that the complete water volume is determined. In addition to the volume of the filter, the amount of water in the bucket is added. The total is then needed to determine the amount of citric acid.


    Powdered citric acid is dosed as described in the instructions on the package or in the leaflet for cleaning coffee makers or kettles - for the exact dosage see the manufacturer's instructions. As a rule, about 40 to 60 g of citric acid powder per liter of water are recommended here. Depending on the total volume of water used (in the filter and bucket) an appropriate amount should be added. The calculated amount is now mixed into the bucket. Over time, and under the influence of the flow, the powder will dissolve in the water.

    Let the filter run for a day or two. The final step is to disassemble the filter and properly rinse all components again. Now they are ready to go.


    Please read and observe the safety instructions of the respective chemical cleaning agent before use. Never mix different detergents! Similarly, it should be clarified with the manufacturer of the filter whether disinfecting with citric acid will affect the warranty. Application at your own risk! We assume no liability for any damage that may occur!