Black flim on toilet tank

I, too, have a low flow toilet and the tank has that black film on it and now it is interfering with the flushing mechanism. It is always getting stuck and it keeps running. I am on well water and have lime, iron and sulpher deposits. What can you do to prevent thi?. We clean it, but it comes back quickly....

It sounds like managnese and it along with the iron should be treated with an iron filter. Is what you call sulfer from a bacteriological source and have you tried shocking the well and house plumbing?