The fluval 501 is even worse. Their filters are not the easiest things in the world to take a part at all in order to service them. My suggestion would be to buy a different brand of filter that is easier to use. The Fluval once you put the top on that's it your screwed and will have to fight forever before getting the darn thing off again! I can't tell you how many times I had to stop myself from smashing it into tiny pieces because that is how mad and frustrated I would get at not being able get the top off.