I recently have had problems due to two Clown Loaches taking a swim up the output unit during the purging process , they got stuck ... long sad story ,lost lots of fish. I have been emailing Hagen, and suggested they take a look at the design , they said I should take the filter back to where it was purchased and ask for a refund if the filter is not doing what it is designed too. Nothing wrong with the filter when it is working to full capacity but when fish can get into the output unit. I have since added the strainer attachment which is also on the intake end , this will prevent any more fish for sneaking up, an easy solution . Unfortunately Hagen didn't feel the need to offer any suggestions ... It may be a good filter but not happy with their customer service. They were more interested in me providing with proof of purchase and nothing else . Just thought I would post this to give a heads up to what has happened and alert other users to a problem which can be fixed with a slight modification, I would hate others to have the same thing occur especially with such adventurous fish such as Clown Loaches..
Gill