From Anisa's Genius House Hacks newsletter.
The water in our township is hard. I used to see a chalky ring forming inside the toilet tank every few months, not just in the bowl.
A plumber friend told me that plain white vinegar handles it better than anything on the market at far less the cost!
It takes five minutes of actual work and does the rest of the job while you do something else entirely. Below is how I use it.
Lift the tank lid and pour in about two cups of plain white vinegar. Let it sit for a few hours, or overnight if the buildup is bad, then flush a couple of times.
The vinegar breaks down the mineral deposits clinging to the inside walls and the working parts, the same buildup that can make a toilet run poorly or flush weakly over time.