The answere to that question may have been or presumably answered to satisfaction. My recent acquisition and experience with API/RENA Filstar pumps is that when fully loaded, with various media, a lower flow rate can be expected (than that commonly claimed). That's not necessarily new news but is provided as a guide line. For our 55-gallon sized aquariums. I have both a XP2 and an XP3 on line, performing two modes of activity. The XP2 is used as a lightly loaded filter and as the source pump for a UV light system. The XP3 is heavily loaded with Mechanical, Biological and Chemical Filtration media and performs very well. Cleaning and priming are an issue for some but I have followed the directions provided and never seem to experience any significant problems. On YouTube you can find that there are several videos relating to the operation and occasional problems users encounter with these XP pumps. Good luck with whichever way you go or as maybe went.Does anybody use the Rena Filstar xP2 Filter? How does it work?