I have had one problem with my FX5. My 7 Kuhli Loaches have shrunk to 3 because they think the intake to the FX5 would be a cool place to hide. I have found 2 alive but the rest ere filtered to death. Other wise it is a Great filter.
75 Gallon Tank. FX5 with Bio Max in bottom container covered with blue fine filter, Purigen and Charcoal in mesh bags covered with mini bio balls in mesh bag in second, prefilter media covered with blue fine filter in top container. 7 Cardinal Tetras, 3 loaches, too many guppies (my daughter took down her 55 and asked me to give them a home), 2 boatine loaches. Tank up for three months - everyones healthy except for my suicide kuhlis...