If your tank is leaning to one side, this stresses the seams of the tank on that side. You may want to level it otherwise you may end up with a seam leak. Seam leaks are enjoyable...they look similar to a drinking fountain purging up from the plastic, glass retainer....well, that's what my 45 did a couple of years ago...oh goody. Equally enjoyable would be to find the seam leak...