Black flim on toilet tank

[Karenb]

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....

 

[LLigetfa]

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?