How do you get rid of buildup under toilet rim?
What is the black stuff under the toilet rim?
Black rings form in the toilet bowl due to hard water. Hard water has minerals that accumulate. When the minerals form in the toilet, they may appear brown, gray or black in color. Toilet bowl rings that appear dark red in color indicate that too much iron is in the water.
Why do toilets get dirty under the rim?
Those colored mineral deposits are possibly caused by the mineral buildup in and around your toilet’s siphon jets located underneath the rim of your toilet bowl. Unclog them first, then continue with regular cleaning.