I just use a 36mm spanner on the right hand side nut. Get a long spanner (eg 450mm) as it needs to be done up tight! .
It's worth replacing the split pin with a 3mm x 72mm R clip - easier to get out next time
Loosen the axle nut and the right hand adjuster. Tighten the left hand adjuster to get the required belt tension then tighten the right hand adjuster to take up any slack.
Check the front edge of the tyre clears the drive belt, if not loosen the left and tighten the right adjusters until you have a couple of mm clearance.
Finally tighten the axle nut as tight as you can then a bit more to get the R clip / split pin in.
