Black stains inside toilet tank

House was on a well. There were pitch black stains inside the toilet tanks. Whole house filter was also black. No stains at any other fixtures. Any ideas?

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Sounds like manganese, in the water…

“Water coming from wells and springs with high iron and/or manganese may appear colorless initially but orange-brown (iron) or black (manganese) stains or particles quickly appear as the water is exposed to oxygen (see Water Testing).”

From: http://extension.psu.edu/natural-resources/water/drinking-water/water-testing/pollutants/iron-and-manganese-in-private-water-systems

Larry nailed it. High manganese levels are fairly common in private wells in the Northeast. Does not affect taste or health but looks nasty in toilet tanks. I had the issue when I bought my house years ago. The only thing that brought the levels down to where there was no longer any staining was the installation on a hydrogen peroxide drip pump followed down the line with a carbon filter. I need to check the pumps hydrogen peroxide levels every six weeks so I do not run out and the carbon filter get replaced every 6 months.

Sulphur also blackens tanks (and metals). Was there an odor?

No odor. Thanks guys.

No odor. Thanks guys.

Agreed.

ps>> Why is there a stopper on a bidet? :neutral: