I posted on this before. I had a wee temper tantrum with one of my fluvals. I hate them. All the 204,304, and 404 garbage.
I had a 304 and two 404's on my tank. Every time I cleaned them out I wanted to throw them out the window. Something would ALWAYS break. Just because of the brittle plastic. The impeller cover clips would snap off, the hose clamps wouldn't work or would break and the things would NEVER CLOSE all the way.
One day a few months back I hit the breaking point...........literally.
See the picture? That was after 3 failed attempts to get it to seal and after breaking a clip to the impeller housing. I think I might have had a small aneurism.
Now I have a FX5.. Still Fluval I know.. but this one SO FAR is great.