Yes limewater will raise kh, pH and calcium slightly.
If you want to just raise kh, good old Arm & hammer baking soda will do. If you want to raise kh and pH, baked baking soda will do the trick.
The original poster already has high kh due to using pH buffers. This is never a good idea long term.
In the winter time when houses are closed up, a pH reading of 7.8 to 7.9 is certainly acceptable and should not be a cause of concern.
