One other thing you can do if you don't want to leave the carboard tube unglued. Open up the back side of the tank shelf by using a dremel or similar tool to make the arc on the shelf a little wider and deeper. I did mine that way the tank will drop down just as the back end of the tank reaches the cardboard tube. I had to do that with mine because I had already glued the cardboard tube in place when I thought about it