Simple add on x-tensioner. The I3 does not have a way to adjust the tension on the x belt. Other tensioners require replacing parts but this one simply slides into place in just a few minutes.
I noticed that the x axis rods were fixed on the motor end but slid through the plastic on the other end. The frame keeps the tension on the x axis belt. If you push on the smooth rods they slide through the mount and tension the belt so that's what this mod does.
The openscad files can be modified (set new values the the variables at the top of the file) if needed.
The U shaped part needs an M3 30mm bolt put through it so that it looks like a tuning fork. It is then inserted into the mount until the clips come through and click into place (see photo).
The outside bar is then placed over the M3 and the ends of the rods. Add a nut and tighten to remove any slack in the belt.