How to adjust the flow rate on the EHEIM Professionel 4+ 250 filter?

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The EHEIM Professionel 4+ 250 filter is equipped with a flow rate adjustment knob called Range Xtender, located on the top of the filter (part 18). This knob allows you to adjust the pump flow rate between cleaning cycles, to maintain a constant flow even if the filter media starts to clog slightly. The nominal flow rate of the filter is 250 l/h.

To correctly identify and locate the Range Xtender, refer to the assembly diagram provided in the manual. The knob has markings indicating the different adjustment levels, from minimum to maximum. It is easily operated without needing to disassemble the filter.

To increase the flow rate, turn the knob gradually clockwise. To decrease it, turn it counterclockwise. Adjustments should be made gradually and especially while the filter is running, as this allows you to immediately observe the effect on the filter's output flow. A flow rate that is too high can stress the fish and disrupt the balance of the aquarium, while an insufficient flow rate (below 100-150 l/h depending on the size of your tank) will compromise the effectiveness of biological filtration.

When cleaning the filter media, the knob allows you to temporarily compensate for the loss of flow due to clogging, without waiting for a complete cleaning. However, the Range Xtender is only a temporary solution: regular cleaning of the filters (every 3 to 6 months, depending on the biological load of your aquarium) remains essential to maintain optimal filtration and avoid a lasting decrease in performance.

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