The extender of the EHEIM professionel 4+ filter is set to NULL (-) at the delivery status. The Extender is NOT active.
If you notice that the flow rate of your filter is diminishing due to soiling, you can open the extender gradually (+).
When activating the extender, you bypass the pre-filter and you can delay the cleaning for some time.
After cleaning the filter material, however, it is important to place the pump head correctly again.
Please proceed as follows: