The eheim professionel 4 350 external filter is a high tech filter that merges high performance with great energy efficiency the filter also includes xtender technology which enables you to counteract blocked filter media and low water flow to make the filter go for longer before it needs to be cleaned simply use the xtender turning button to redirect the water flow this innovation means that when the eheim professonel 4 350 gets dirty you dont need to clean it straightaway the xtender t