Turn water supply off to toilet. Flush to empty the tank. I have read that this should be done at least twice a year.
White vinegar is a good cleaner for mineral buildup.
Bar Keeper's Friend is also a handy powdered cleanser to have on hand. It will also remove rust and iron stains. Flush to empty the tank. I have read that this should be done at least twice a year. White vinegar is a good cleaner for mineral buildup.