It's time to change the media, but someone else set this up for me and I'm having a tough time getting the lid off! I've shut down the nozzles, disconnected and unplugged, brought it into the kitchen sink, unhooked the metal clamps and for the life of me can't get the top off? The gray plastic top should come all the way off like this, I believe:
http://eheim.com/base/eheim/DBimages...77757_Kopf.jpg

I know this is a ridiculous question, but am I missing something? Does it just need more elbow grease?