We have a toilet that we do not use very often and because of this we get a scale ring in that is hard to remove.
To get rid of the scale from this ring we take toilet paper and place it on the scale. After you place the toilet paper you will need to spray 100% vinegar solution on to the toilet paper and let it sit for at least 15 minutes.
Flush the toilet and scrub the effected area, the limescale will be removed or reduced. Repeat if required till all the scale is gone.