Black Spots In The Toilet Bowl? (Possible Causes & Fixes)

Matthew Mountain
by Matthew Mountain

If you open up your toilet and for the first time notice several black spots in the bowl, it’s likely you’ll wonder what these are and whether or not they need to be taken care of. In most cases, the black spots are either mineral deposits or mold growth.

Whereas one group of black spots is only harmful to the toilet, the other group is harmful to humans and toilets alike. In this article, the black spots that can manifest in a toilet bowl will be identified and explained. Removal procedures and other useful information will be put forward as well.

The black spots that sometimes manifest in a toilet bowl are usually either hard water stains (manganese) or black mold. When you notice the black spots, you should immediately take steps to get rid of these. If you’re dealing with mold, you’ll definitely need to remove this, as this growth can not only damage your toilet but harm you as well.

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What Are the Black Spots?

Determining what the black spots are is important, and it was already mentioned that these spots are likely either mineral deposits or mold growth. Mineral deposits are also known as hard water stains, and these can appear on sink and shower drains as well as toilets.

These stains manifest when there’s prolonged exposure to minerals in the water supply. If mineral buildup is not addressed promptly, it will damage the toilet and look more unsightly by the day.

If the black spots are indeed mineral deposits, then it’s quite likely you’re dealing with manganese. This mineral will create a black ring around the toilet, but the good thing is that it’s removable, even on a DIY basis.

Removing Manganese From the Toilet

Below are the items you’ll need to get rid of manganese:

  • Borax
  • Distilled white vinegar
  • A Spray bottle
  • A Toilet brush
  • A Cup (optional)
  • Cream of tartar
  • Three-percent hydrogen peroxide
  • Toothbrush

Note: You should use borax because it’s gentler than acid cleaners and not as toxic as bleach. Also, you should wear a face mask while cleaning, and goggles can be worn as well (though these aren’t required).

To remove manganese spots from the toilet, first turn off the water supply. If the spots are beneath the water level, then flush the toilet and make sure the area around the spots is dry. Once it is, mix cream of tartar with three-percent hydrogen peroxide until a thick paste is formed.

Now apply this paste to the spots using a toothbrush. Let the paste sit for about 15 minutes. Once the time has gone by, rinse the paste off with a cup of water.

If some black spots are still there after the rinse, simply repeat the process until there are no more spots. Once they’re all gone, do one final rinse and then turn the water back on. You should be good to go!

Black Mold Background

If the spots are not manganese—and you know this right away—then you should be preparing to remove mold from your toilet bowl. Mold can also grow behind, underneath, or inside the toilet’s tank. It’s usually black though sometimes it can be green or orange.

Mold will thrive in a bathroom, as bathrooms are usually damp and poorly ventilated. Mold also likes to grow where there’s stagnant water.

When you notice mold in the toilet, it’s best to get this taken care of right away, as mold can spread fast and be quite harmful to humans. Below, the things that cause black mold to appear in a toilet are explained. A thorough removal procedure is put forward as well.

Before you go and start removing mold on your own, you should first consider hiring a professional, as they have the know-how, tools, and cleaning products necessary to get rid of black mold completely, no matter where it is.

What Causes Black Mold?

Black mold is not caused by one thing alone, and this is why combating it can be difficult. Below are the most common causes of black mold growth.

Infrequent Toilet Use

This will almost definitely lead to black mold growth. The toilet is a perfect home for black mold, as there’s stagnant water, it’s moist, and the temperature is warm. And if you don’t flush the toilet often, the chlorine won’t have a chance to combat the mold. As a result, this repulsive and harmful growth will spread.

Stagnant Water

The tank, which is often overlooked, can be a great home for black mold, especially if it’s not cleaned regularly. This is because there’s stagnant water in the tank. Mold will feed off algae and other nutrients that are found in stagnant water. Another thing that makes the tank an ideal home for mold growth is that it’s dark.

Although it may seem like a hassle, make cleaning the tank a part of your toilet cleaning routine. Preventing mold growth is definitely worth it.

Mineral Buildup

If there are mineral deposits on the tank walls, the mold will feed on these. As was mentioned before, hard water has high mineral concentration. Therefore, if your water is softer, then mineral buildup shouldn’t be a problem. The key here is to tackle the mold problem as soon as you identify it. If the situation is not handled promptly, the mold will feed on the mineral buildup and expand unchecked.

Worn-Out Washer

If you find mold under the tank, it’s likely because water has been passing through the washer, creating the ideal conditions for mold growth. Unfortunately, faulty washers are often identified when it’s too late. This is another reason why routine cleaning is important. You wouldn’t have cause to look at the washer otherwise, so you’d never know if mold was growing unimpeded.

Leaving Waste in the Bowl

Not disposing of waste immediately after it enters the bowl can also lead to mold growth. This is one important reason why you should never forget to flush!

Bad Water Supply & Rusty Pipes

If your home’s water supply is bad, then your pipes are likely rusted and therefore a breeding ground for mold and other fungi. If mold growth is coming from the pipes, you’ll notice spreading first around the toilet’s tank.


If the bowl is cracked, then a leak can spring and create a perfect environment for mold to flourish in. This is one reason why, when you notice a leak, you should find its source immediately. The leak is most likely coming from a crack.

Removing Black Mold From the Bowl

To get rid of black mold, you’ll need the following items:

  • GlovesA Face maskA BucketRagsVinegarBoraxBaking sodaBleach

Before you begin cleaning, open the doors and windows so the bathroom is ventilated well. You’ll be working with chemicals that may emit noxious fumes.

Step-By-Step Process

  • Once you have your safety gear on, turn off the water supply and flush the toilet. Flush until the tank is empty. This way you get a clear view of the mold.
  • The first thing you must do is pour drain cleaner at the far end of the bowl, as this way it’ll go down the drain.
  • Next, sprinkle some baking soda or borax on the bowl while paying close attention to the waterline.
  • Now spray some vinegar over the baking soda and then scrub this gently by hand or with a brush, e.g. an old toothbrush. You can also use a toilet brush or a nail brush. Scrubbing will require considerable energy, as it takes time to remove the fungus.
  • Now, wait a half-hour to an hour.
  • When you come back, scrub again.
  • Now rinse out the toilet with a cup of water.
  • Next, add bleach and then wait another hour.
  • After the hour goes by, pour hot water into the toilet bowl to further activate the bleach.
  • Now flush the toilet.

Repeat this process until the mold is gone.

Something Else to Keep In Mind

It’s best to follow this procedure when you first notice the mold. If the mold has plenty of time to get entrenched, then getting rid of it will be considerably more challenging.

This does not mean that dug-in mold is impossible to get rid of. You’ll just need to get help from a mold removal expert.

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Related Questions

What’s the pink stuff in the toilet?

Although serratia marcescens bacteria is often pink, sometimes it can look dark brown or even black, especially if there’s a lot of it. This can be found in human waste, soil, and dust, and it grows in moist conditions.This stuff isn’t harmful but it makes the toilet look unsightly and unsanitary. If you clean your toilet regularly, you won’t have to worry about this. Just use standard toilet disinfectant—this will keep the bacteria away.

How often should the toilet be cleaned?

Cleaning a toilet once a week is best, but most homeowners do toilet cleaning biweekly. It doesn’t take long to clean a toilet effectively; you just need the right products and tools. Proper disinfecting will keep your toilet in good shape and also keep you healthy.

Matthew Mountain
Matthew Mountain

Matt loves everything DIY. He has been learning and practicing different trades since he was a kid, and he's often the first one called when a friend or family member needs a helping hand at home. Matt loves to work with wood and stone, and landscaping is by far his most favorite pastime.

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