muratic acid
try this stuff at your own risk.... it works great!
But you need plenty of ventialtion in the room too.
this stuff will clean any bowl down to the original luster....
buy a gallon at any hardware store 3.50
bail out the toilet bowl of water,, then
pour a gallon into the bowl.
cover the bowl off with a plastic garbage bag so the fumes wont get out into the room --- the stuff actually sort of hisses as it is cleaning the lime out of the bowls innards.
WARNING! It will discolor and pit chrome!! you must cover the bowl with a PLASTIC garbage bag to seal it off as best possible, .
the room must have ventialtion ..turn on the fan and open a window.
its not all that nasty, but the smell will make you cough.
Its used to clean concrete.
let it sit for as long as possible
fulsh it down the drain and flush it 4 or more times just to dilloute the acid....
I was amazed on how well it will totally scour out a bowl.
we use it often to actually clean out the trap of an old toilet that isnt flushing well anymore... it makes it flush like the day it was installed.
again attempt this at your own risk.