How to Remove Black Mold in Toilet Tank & Bowl

Mold and mildew manifest in your toilet either inside, behind or under the toilet bowl or tank as a black ring or spores or streaks streaming down the bowl. The discoloration could change over time to different colors such as green or orange, but the most common one is black.

Their infestation is caused by dampness, stagnant water, and poorly ventilated toilets. While they are unsightly to see they also impose a back image on your levels of hygiene, which is why it is essential that to remove them as soon as you spot them. Following is a detailed guide on how to deal with the mold including preventive measures and answers to commonly asked queries.

What Causes Black Mold in the Tank?

As mentioned above the toilet tank too can get a mold infection for various reasons. The most common causes include,

  • Stagnant water – the tank is a neglected area of the toilet. As so, the area never gets cleaned out leaving it safe for the mold to grow, leaving them to feed on algae and other nutrients found in stagnant water.
  • Darkness – yes, when the lid is added to the tank, the mold tends it thrive more since it’s an opportunistic fungus that doesn’t require chlorophyll acquired from sunlight.
  • Mineral deposits – the more water stays put in the tank, the more deposits shall gather in the tank causing mold to infest more and more. Sometimes the condition is worsened by the type of water in that hard water contains more minerals than soft.
  • Worn-out washer – this is prevalent if you see there’s mold underneath the tank. The purpose of the washer is to seal water from passing through. So if the area has mold, it means there’s some form of leakage and the washer no longer does its job adequately.
Black mold behing tank of toilet
Mold behind tank
Black mold below tank
Mold below tank

How to Remove Black Mold in the Water Tank

Once you’ve spotted the mold from the water tank, you need to clean out the area thoroughly to get rid of the mold. There are several ways you can do that, including simple DIY ingredients such as vinegar or lemon juice mixed with baking soda.

Materials Needed

  • Soft hand brush
  • Vinegar
  • Bleach


  1. Flush out water from the tank while turning off the water inlet. Ensure the tank remains empty for some time.
  2. Pour in vinegar into the water tank by spraying. Make sure all the corners are attended to. Leave on for half an hour.
  3. Scrub the toilet tank gently to scrape off any mold that may not have come out yet.
  4. Turn on the water outlet and let the water fill up again. Add some bleach and let sit for another half an hour.
  5. Flush the water and check to see if the mold has cleared. If not, repeat until you achieve the results.

It is vital to note that the bleach or vinegar can affect some parts in the tank hence one needs to be prudent about how they add in the bleach or vinegar to the water.

How to Remove Mold Behind Toilet Tank

When water drips at the back of the toilet tank, mold can grow there as well. Luckily, removing mold from behind the tank is simpler. Here’s how:

Materials Needed

  • Bucket or container
  • Rags
  • Soft hand brush
  • Vinegar
  • Baking soda
  • Disinfectant/ Bleach


  1. Wipe down the back of the toilet tank to get a clear glimpse of where the mold is.
  2. Make a paste in a dish using baking soda and vinegar. Ensure the paste is thick enough to stick behind the toilet tank.
  3. Apply the paste over the mold-infested areas ensuring to cover each and every section of the back area.
  4. You can scrub gently with the hand brush to make sure the paste gets in between the grout areas of the tank.
  5. Leave it on for half an hour.
  6. Once back, scrub the back of the toilet gently to scrape off the mold that may not have come out yet.
  7. Wipe down with a rag to see any areas that may need further scrubbing.  Continue until you have your results.
  8. Spray clean water on the area for a clean finish. You can also add some bleach to disinfect.
  9. If the mold spots or stains haven’t cleared, repeat until you achieve the results you want.

Mold (Black Spots) in Toilet Bowl at & Below Water Line

You have read about mold stains in the toilet tank and behind the tank. Now let’s see how we can deal with mold stains found inside the toilet bowl either at or below the waterline.

Mold forming at the water line can be an indication that you rarely use the toilet, which has then made the area conducive for the growth of the mold.

It could also mean that the drainage is completely dirty and its time for a thorough clean up. Finally, when there’s mold below the waterline, it means you have a plumbing issue.

Dealing with Black mold toilet bowl
A toilet bowl with black mold


As you have read above, the main reason why you have the ring of mold at the water like of the toilet bowl is that there is an accumulation of dirt which has led to mold growth. The stain/ ring is not permanent, hence it should come right off once you indulge in some thorough cleaning with the necessary materials as you shall read below.

When mold grows below the water line and more around the base of the toilet bowl, it could mean you have a broken water seal that needs immediate attention from the plumber. The broken seal means the area is experiencing a leak underneath or from the water inlet.

A leak then means a damp area and a conducive environment for growth and development of mold. The plumber will need to replace the wax ring to stop the leak then you can clean the area off the mold and that’s all.

Steps to Remove the Spots

If you want to remove the mold spots from your toilet bowl, here’s an in-depth look at the method you can use. Remembers mold may not directly affect your health but prolonged exposure to its spores can cause you adverse allergic reactions.


Step 1: Assembly and Preparations

Put together all the essential items you will need like protective clothing – gloves, a breathing mask, clothing such as rags. Take buckets and household cleaners as well. Open the door and windows for the bathroom area to ensure the room is properly ventilated. You could also get some vinegar, borax, baking soda, and a cup of bleach for a thorough clean.

Step 2: Cleaning the Mold Spots

  1. Start off by flushing the toilet for a clear view of the mold spots.
  2. Rinse out all the water from inside the bowl to view the water like and the base of the toilet.
  3. Add in the drain cleaner first at the fat end of the bowl so it goes down the drain.
  4. Sprinkle some baking soda or borax on the bowl with added attention to the waterline.
  5. Continuously spray vinegar over the baking soda and scrub gently with a hand brush, old toothbrush or a nail brush. Clean it for some time to loosen the fungus.
  6. Leave for about half an hour to an hour.
  7. Come back, scrub again, then flush the toilet for a clean rinse.
  8. Add in some bleach to the water and leave unattended for another hour.
  9. After that, pour in sparkling hot water to the bowl to activate the bleach further, then flush the toilet.
  10. If unsatisfied with the results, repeat the procedure several times. Clean up your cleaning items when done.

This procedure is only best at the first instance of sighting the mold infestation. After that, regular cleaning can prevent the need for aggressive cleaning.

Prevention Measures

To avoid any further infestations of mold, use these simple preventive measures.

  • Ventilate the bathroom during and after you take a shower. This is because the area is damp, which then inhibits the growth of mold. Opening the windows or using a fan keeps the area cool.
  • Use dehumidifiers when you can open the window such as at night or maybe during a cold season.
  • Always clean up after using the toilet. Flushing down your waste even after using it for a short call.
  • Regularly clean the toilet using scrubs and chlorinated cleaners.
  • Fix any bathroom leaks as soon as they start.


Why is Mold Growing in My Toilet?

Mold thrives on organic surfaces such as the toilet’s tank or behind the tank because of the hard water deposits found there. They offer a conducive environment for growth, not to mention a continuous supply of nutrients for the mold.

Urine with some levels of ph, chemicals from human waste, and rust in the pipes are some of the reasons why mold is persistently growing in your toilet.

Another reason could be cracks and crevices on the toilet or tank. The spacing allows for mold to grow themselves onto the toilet while the other elements keep them flourishing.

Alternatively, if the toilet is not in use, the area then becomes warm, which is also another excellent breeding condition for mold. Besides, no use means not cleaning up and the chlorinated water used to keep off the mold will no longer be active.

Is Toilet Mold Dangerous?

The back mold growing in the tank, behind it, and under the toilet bowl is not dangerous. However, it could cause allergic reactions to some people. The only downside to having mold in the toilet is its unsightly nature, otherwise, it’s not toxic nor does it cause direct infections to someone.

Can Mold in Toilet Make You Sick?

As mentioned above, the mold in the toilet is non-toxic unless you are allergic to it. However, it is recommended that you have safety measures put in place so as not to encourage its growth. You could put on a respirator so the spores from the mold don’t trigger allergic reactions as you clean.

Also, use other protective clothing such as gloves, clothing, and safety glasses for added protection. Clean the bathroom with the windows open for better ventilation.

Mold in Toilet Bowl & Diabetes

There’s no direct link between mold and diabetes. That’s to mean mold doesn’t cause you to get diabetes, but the mold could highlight certain symptoms from your body. How?

Well, mold thrives in sugar and as we all know, when one is suffering from diabetes, the body doesn’t adequately hold on to enough glucose but rather releases it through urine.

Hence, when you notice a reoccurrence of mold in your toilet with all other factors standard, it could mean your urine contains too much sugar meaning you may be suffering from diabetes even without your knowledge.

The link then appears in that mold infestation could be a major indication of your blood sugar levels in sweat and urine, warranting the need for a checkup.

Further Reading

One Comment

  1. Hello my friend! I want to say that this post is amazing, nice written and include almost all vital infos. I would like to see more posts like this. Mariele Isadore Donny

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