I'm sure most people have struggled to level an aquarium stand at some point, though in the past I've been pretty fortunate to automagically set up a stand and find it almost perfectly level. I moved in to a new house a couple of weeks ago and found I was not quite as fortunate...The house itself seems sound, and the location for the aquarium sits right on top of a cross beam in the flooring, so I know the floor boards aren't simply junk which has caused the uneven flooring. I tried shims to level it out, but the slope was just too much, and I was starting to loose stability of the stand by needing to raise one end so much.
So, I decided to build a platform that the aquarium stand would sit on that would correct for the slope of the floor. I cut an 8ft length of 2x4 in half to match the 4ft length of the stand, and then measuring the height difference from one end of the uneven stand to the other let me cut diagonally across this 4ft length with the slope to correct for it. Using a belt sander, I then smoothed down these edges which would be face down on the floor when the platform was complete. I used a 3/4" pine board to match the aquarium stand, and it was only a couple of dollars more than a sheet of plywood. Here's a couple of photos showing how it came together:
When I placed the stand on top of this platform and set my trusty spirit level on, lo and behold, a level surface for my 55g to now sit on
The little alcove the aquarium sits in really does mess with your eyes when you look at the angles of the walls and floor boards, but at least the aquarium is level and the floor hasn't collapsed in protest