The Causes And Solutions To Black Mold In Toilet Bowl And Tank

The Causes And Solutions To Black Mold In Toilet Bowl And Tank

Many people will have had this problem before. You’ve gone into your bathroom and noticed a build up of black mold around your toilet bowl and in your toilet tank. 

This is unsightly and unsanitary, and can become dangerous if nothing is done.

Luckily though, there are some excellent solutions to this problem. Of course though, you’ll need to understand what the causes are of this black mold first.

Fortunately for you, I’ve written this comprehensive guide that explains everything you need to know. I’ll cover all of the causes of this black mold in your toilet and explain how you can resolve the problem.

Ready to learn more? Then read on and discover the answers.

What Is Black Mold?

Black mold, which despite its name can often appear orange or green, is a type of fungus that grows in moist, warm and dark locations.

This is why black mold is quite common to see in bathrooms due to the humidity, especially when ventilation is poor.

Black mold is often found in toilet bowls, toilet tanks, shower heads, bath tubs and similar areas.

Without removal, black mold can lead to significant further growth in the surrounding areas and even lead to respiratory problems, particularly with younger people or vulnerable people.

Causes Of Black Mold

The Causes And Solutions To Black Mold In Toilet Bowl And Tank

I’ll start this guide by explaining the causes of black mold in your toilet. It’s critical to understand why this might be happening first, as prevention is as important as the solution. 

It’s important that I first clear something up. Brown stains which are commonly found in toilet bowls may be a separate problem, which is often due to poor water quality.

This type of stain should easily be resolved with bleach, flushing and scrubbing with a toilet brush.

Infrequent Flushing 

When water remains stagnant in locations like a toilet bowl, mold can rapidly grow.

As a toilet bowl by its very nature has stagnant water, this problem can quickly occur. This is because of the warm and moist environment which increases the risk of chlorination. 

As a result, frequent (or normal) use of the toilet flush can change the water and prevent chlorination – which helps to prevent any growth of mold. 

Dark Areas 

Mold is a type of fungus that does not require chlorophyll to grow (which would normally come from the sun). 

As such, when the fungus is left in darkness (like a closed lid), it finds a perfect opportunity to thrive. 

When the toilet is left for a while in darkness and without any action taken, the mold will continue to grow more and more.


Mineral deposits can actually feed mold as it acts as nutrition. Mineral deposits are abundant in the walls of the tank and in stagnant, hard water.

Of course, the more minerals that are present – the more nutrients the mold will receive and the more it will grow.

It’s worth noting that hard water is a significant factor to this, as it contains more minerals than soft water – so it will depend on where you live for this to be a primary source of the problem.

Residual Human Waste 

When a toilet still has human waste present (whether you can see it or not), mold is encouraged to grow.

This is especially the case if the human waste contains a lot of sugar, as mold grows quicker when exposed to sugar. 

Faulty Washer 

When your washer is broken or worn-out, it cannot do its intended job of stopping water from passing through. As a result, mold can easily grow in the conditions that the water causes. This is more seen underneath the tank.

The Pipes For Water Supply

Another potential cause of mold in your toilet is the pipes that allow for the supply of water.

When the pipes are rusty, condensation can occur which becomes a strong breeding ground for mold. If you have recurring black mold, this could be the culprit.

Damage To Your Toilet 

Any cracks, breaks or small holes in the bowl or tank can become a conducive area for mold to grow healthily. If this is the problem, you will need to source a replacement of the entire unit.

Black Stains Under The Rim 

It’s common for people to see black stains underneath the toilet rim or underneath the waterline etc.

If black mold is forming on the waterline, this is typically indicative of infrequent use of the toilet. When this is the case, a powerful clean up is required. 

However, if black mold is growing below the waterline, this is generally due to a broken or faulty seal, which means you will need to get a plumber to your house to fix the issue. The same applies if you notice any significant leaks coming from the toilet. 

Cleaning Up 

If you are sure that the problem is due to infrequent use of the toilet, there are some simple ways you can clean up. You’re going to need the following items though before you start:

  • Protective clothing and equipment (such as a mask, rubber gloves, and goggles) 
  • A toilet brush and rags 
  • Cleaning solutions (such as vinegar, bleach, baking soda and steam cleaner)

Depending on the severity of your problem, you may need to carry out a variety of cleaning methods, or one may work on its own. I’ll show you now how to perform each one. 

1. Vinegar 

If you opt to use vinegar as your primary cleaning solution, you will need to follow these steps:

  • Properly ventilate the area by opening all the doors and windows 
  • Put on your protective gear 
  • Flush the toilet to remove any easy-to-remove residue 
  • Spray the bowl with vinegar using a spray bottle, and allow it to sit for 15 minutes
  • Scrub the affected areas 
  • Repeat 
  • Clean all of your used items 
2. Baking Soda And Vinegar 

If your stains and mold are more stubborn, you can add baking soda to your vinegar solution. Follow the steps above as before but allow the solution to sit on the bowl for 60 minutes instead of 15. 

You will need to scrub more gently and you may be better off using an old toothbrush for this step.

After you have done this, apply some bleach, allow a 15 minute gap of time and then flush the toilet. If the problem persists, repeat. 

3. Steam Cleaner 

If you’re hoping for a way to clean your toilet without the need for chemicals, then you may decide to use a steam cleaner. Once you’ve got yourself one of these, follow the steps:

  • Empty the bowl entirely 
  • Wear protective clothing
  • Angle your nozzle to all of the hard-to-get areas and work downwards 
  • Do this on all areas with mold present, including hinges etc.
  • Spray the area with vinegar to remove any leftover debris 
  • Flush the toilet 

If the mold is still present, simply repeat the step – however this generally tends to do the trick.

How To Remove Black Mold From Toilet Tank

Now, I’ll take you through some of the ways to remove black mold from your toilet tank.

If you have spotted this mold present, you need to immediately and thoroughly clean out your toilet tank so it cannot move to and reach your toilet bowl. 

Luckily, there are a few options for this. Before you start though, you’re going to need to get yourself a soft hand brush and some vinegar. 

As with some of the previous steps, you will need to allow the vinegar to settle onto the tank for around 30 minutes. After this, you will need to flush your tank several times and scrub the tank as much as possible.

Continue to this until all the mold has been removed. Once again, if vinegar alone is not getting the job done, you can add baking soda to the mixture. However, ensure you do not use bleach in the tank.

How To Remove Black Mold From Behind Toilet Tank

If you notice black mold is behind the toilet tank though, this is likely due to water escaping and dripping behind it. In order to remove this, you will need to create a cleaning paste using vinegar and baking soda within a dish.

Next, apply the paste to all affected areas and allow it to sit for about 60 minutes. After this time, scrub and scrape all the mold off thoroughly and continue to do this until you get rid of all of the black mold.

Once this has been done, spray fresh, clean water around the area with a bit of bleach in the solution. This will disinfect the rest of the area. You need to ensure that this area is not only free of mold, but is also dry before you finish.

If the problem persists, repeat all of these steps until you manage to completely clear the area of black mold. Don’t forget to wear protective clothing and wash your hands after you have finished. 

Preventing Black Mold From Returning 

The Causes And Solutions To Black Mold In Toilet Bowl And Tank

One of the best things you can do to fight against black mold is prevention. If you can prevent black mold from coming back, you should not need to carry out long and arduous cleaning. 

Here are some of the best steps that you can take to prevent the build up and growth of black mold. 

Ensure Proper Ventilation 

As I mentioned earlier, one of the biggest reasons why black mold builds up is because of moist and warm environments. Generally speaking, toilets are located in bathrooms which may have showers or baths. 

As a result, a build up of warm moisture can occur and this can lead to black mold everywhere. Even when a toilet is located in a separate room, the area can still be warm and full of moisture. 

Therefore, a great preventative measure is to ensure that you properly ventilate the area. After all uses of the shower, ensure you open a window or switch on the extractor fan. Do this until all clear and obvious moisture has escaped the area. 

If a toilet is in its own room, allow the air to escape by keeping the seat up every now and then and switch on the extractor if you have one. Dehumidifiers can also be a great choice if you have no other options.

Allow For Natural Lighting 

Black mold is less likely to grow in naturally well-lit areas. If you can, ensure the toilet is exposed to natural light for parts of the day. If your bathroom is especially dark, it might be time to change your windows and allow for more light to shine in.

Regular Use 

As I said earlier, stagnant water and infrequent use of the toilet can quickly lead to mold. Ensure you use your toilet and flush it regularly.

If for any reason you are not going to be using your toilet for an extended period of time, it’s a good idea to ask someone to do it for you.

If a toilet is in a separate room and is not used that often, try to remember to flush the system every now and then. 

Regular Cleaning 

Perhaps the best preventive measure of black mold is to clean the toilet area regularly. Many people set up a cleaning schedule and ensure their toilet is part of the cleaning itinerary. 

Use toilet bleach and scrub the toilet when it is required. These items are relatively inexpensive and can save you a lot of money in the long run.

Check For Damages Regularly 

Always try to pay attention to your bathroom items and check to see if there are any obvious damages.

If there are – you need to address them as soon as possible to avoid any mold growth and other related problems. 

If you have noticed something, you should contact a professional to ensure your system is fixed and clean, allowing for future use. This also applies to the pipes which are showing any signs of rust.

Prevent Condensation

Condensation is a regular occurrence but you can protect the bathroom from black mold build up by covering cold surfaces with a cloth and regularly changing them.

It’s also a good idea to ask a professional about protection during winter months at the same time. 

This can prevent water pipes from cracking, which can quickly lead to the growth of mold.

Change Things Up Regularly 

When I say regularly, I don’t mean every week. But having an idea of modernizing your bathroom every few years and repainting or retiling the bathroom at the same time can be an excellent way to protect your bathroom from black mold. 

This also applies to your windows and towel heaters (if you have them). It’s critical that you do not try to paint over moldy areas as this will cause cracks to the paint and lead to even further problems. 

Inspect After Cleaning 

It’s always a good idea to inspect the areas after you have cleaned them on a regular basis to ensure there is no obvious build up of black mold. Some people think that once the cleaning is complete, that’s it – but this couldn’t be further from the truth! 

Love Your Bathroom! 

Above all else, you need to ensure that you love your bathroom and you take care of it regularly. After every use, make sure you follow these steps above and keep your bathroom looking and feeling its best.

Frequently Asked Questions 

Why is black stuff coming out after flushing?

There could be a variety of reasons for this, including black mold being present, rusty pipes or even the water itself being dirty.

Is black mold harmful?

The EPA states that black mold can lead to flu like symptoms and it can be very harmful in large amounts to vulnerable people.

Is it safe to clean black mold yourself?

Homeowners can handle cleaning about 10 square feet (roughly 3 feet by 3 feet) of black mold on their own. If the patch is small enough, a combination of bleach, water, scrubbing, and ventilation should do the trick. Before treating mold on your own, prioritize ventilation and protective gear.

Can you sleep in a house with black mold?

So, if you are sleeping in a damp or mouldy room, you’re spending about a third of your time inhaling dangerous mycotoxins spores. Frequently inhaling these spores leads to a plethora of health problems for both healthy and vulnerable people.

Final Thoughts 

Black mold in your toilet is annoying but you don’t have to live with it. If you follow these pointers above, you should be able to identify the problem, where it is coming from, why it happens and how to deal with it, along with how to prevent it again!

Adrienne Carrie Hubbard

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