Disgusting-looking toilet issue that isn't actually disgusting

[potato80]

Help!

An upstairs toilet that never gets used looks like this (attached).

It looks dirty, but actually isn't. It seems to be stained or scuffed or something, below the water line.

Can anyone help identify the problem, please?

Thanks

 

[Madrab]

Scale/deposits from the water, if the pan rarely gets used the water will evaporate leaving behind scale and deposits that build up inside the cistern. Once cleaned up flush the toilet once a day and it shouldn't return.

 

[EddieM]

Tip a litre of coca cola in it.

 

[potato80]

What a shame; I was planning on blaming my mother-in-law.