I noticed that mine was pretty slack as well, especially after using it a couple times.

I pulled up on the arm of the sander to tighten it up as much as possible, then "pushed" in carefully with the blade to take up any remaining slack. It put a little more pressure on the blade while honing, but this is the leather belt, not one of the 150 grits, so I figured it'd be okay. If anything, the little extra pressure against the belt and blade helped the honing put that mirror finish on the edge.