What Is the Black Stuff Around the Rim of Toilets?

A black ring around the toilet rim makes your toilet look unsanitary. You may end up scrubbing the black stuff off the toilet, only to find that it has returned two to three days later. The black discoloration that forms often indicates a problem with the water, such as mold spores, bacteria or minerals. Cleaning the toilet regularly and treating the problem will help keep your toilet in good condition.

...
Remove the black stuff around your toilet rim with common household items.

Mold

Mold has dangerous spores that can irritate the lungs, throat and sinuses. The fungus grows best in areas that are dark, warm and moist. Mold releases spores that continue to grow and multiply. The mold may appear black, green or even orange in color and form a ring in the toilet bowl. When you notice mold, remove it as soon as possible to prevent it from spreading. The mold may take over the toilet bowl and make it look dirty if you do not take the time to clean it properly.

Mineral Deposits

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. If you determine that hard water has caused the stain, you can remove it with common household products. Treating your water with a water softener helps prevent these rings from forming.

Bacteria

Serratia marcescens bacteria often appear pink in color but could appear dark brown or black if they accumulate. The bacterium resides in feces, soil and dust and grows in moist locations. The bacteria often remain harmless but can leave your toilet looking unsanitary. Cleaning the toilet regularly helps control it, but it may be impossible to remove it entirely. Repeated cleaning and disinfecting helps destroy the bacteria and ensures that it does not return.

Solutions

Clean the toilet bowl frequently with a toilet brush. Disinfect the toilet bowl rim by pouring 1/4-cup chlorine bleach into the tank to remove mold and serratia marcescens. Allow the bleach to sit for 10 to 20 minutes and then flush the toilet twice to rinse the bowl and disinfect it. Pour 1/4-cup white vinegar and 1 cup of borax into the toilet bowl and allow it to sit overnight to remove mineral deposits. Scrub the toilet the following morning.