The EHEIM professionel 4 EHEIMs best external filter but now with an integrated ‘emergency’ button. They have adopted the many advantages of the professional 3 series – powerful performance, optimal energy efficiency, quiet operation, priming aid, safety hose adapter – but they have also improved the technology by incorporating the new ‘Xtender’ button. In the event the output is reduced due to the fine filter media blocking, the button can be adjusted to redirect the flow. The biological filtra