Why Is There Mold In My Toilet Tank?

Most people don’t often think about their toilet tank until they must remove the lid. Naturally, finding mold in the toilet tank can be quite concerning. So, you may wonder, 'why is there mold in my toilet tank'?

If there’s mold in your toilet tank, it’s likely because you haven’t cleaned it in a while. The water in a toilet tank typically stays stagnant for extended periods and often contains lots of bacteria. That, paired with the darkness, can contribute to mold growth. Clean the tank every few months to reduce the risk of mold.

Improving the lighting and ventilation in your bathroom can significantly reduce the risk of mold growing as well. It’s important to remove mold from your toilet tank before it spreads throughout your house. Follow along as we explore what causes mold in a toilet tank and highlight ways to treat it.

What Causes Mold In A Toilet Tank?

1. Limited Use

Limited use of a toilet is the main reason for mold in the tank, and that’s especially true in guest bathrooms. You’re more likely to find mold in a toilet tank in bathrooms that you don’t use often. For most people, that includes guest bathrooms, as they may go weeks or months without being used. The longer the water is stagnant, the more likely mold will form in the toilet tank. Mold loves stagnant water because it’s easier for spores to multiply in that environment. That’s especially true when you consider that toilet tanks are also dark.

Darkness and moisture are two essential ingredients to create mold. Naturally, this darkness and moisture will go undisturbed in a toilet you don’t use. You can prevent this problem by regularly flushing and maintaining each toilet in your house.

2. Poor Maintenance Habits

Nobody looks forward to cleaning a toilet, but it’s necessary, whether you rent or own your home. That said, many people clean their toilet bowls and stop there without thinking about the tank. This can explain why you find mold in the toilet tank. You don’t need to clean your toilet tank as much as the bowl, but it’s still necessary. Even just cleaning your toilet tank a few times per year can help prevent mold growth. Not only will this help prevent mold, but it can also help get rid of mineral deposits in the tank.

Otherwise, your toilet tank can quickly become corroded, especially if you live in a house with hard water. To clean the toilet tank, flush the toilet, then fill the tank with up to 2 gallons of white vinegar. Let it sit overnight, scrub the tank with a brush, and repeat this process every few months if you struggle with mold.

3. Weak Ventilation

Mold loves poor airflow, as stagnant air helps it grow as much as standing water does. Your bathroom is already humid from the sink, shower, and toilet, so stale air creates a deadly combination. This can result in mold growing in your toilet tank and even the bowl itself. You can fight this problem if you improve the ventilation in the bathroom. The best way to do this is to run the ceiling fan during showers and for 30 minutes after each shower. If you don’t have a bathroom fan, install one to improve the ventilation and indoor air quality.

That may not be an option for you, but you can at least run a dehumidifier to prevent mold in the bathroom. The indoor air quality in your bathroom should never exceed 50%, as that can contribute to mold. Set your dehumidifier to maintain a 30% to 50% indoor humidity level throughout your home, including the bathroom.

4. Improve The Lighting

Darkness is mold’s best friend, and toilet tanks are constantly dark. You can’t necessarily put a light in your toilet tank, but you can improve the overall lighting in your bathroom. Doing so can make your bathroom less comfortable for mold, reducing the chance of it growing in the toilet tank. If possible, increase the natural light in your bathroom by uncovering the window. Some bathrooms don’t have windows, so that’s not an option. However, you can at least install warm, daylight-temperature lightbulbs to improve the lighting. It also helps to add some reflective surfaces throughout your bathroom beyond the mirror. For example, hanging pictures and covering the walls with glossy paint can help reflect light.

Is Mold In A Toilet Tank Normal?

Mold in a toilet tank is normal, but that doesn’t mean you should leave it alone. There’s a good chance the mold can spread into the rest of your bathroom. Once that happens, it can easily spread throughout your house and cause problems. You can’t see mold spores with the naked eye when they travel throughout your home. When the AC or furnace runs, the air can carry the mold spores from room to room. Once they enter the air ducts, there’s no limit to how far the mold spores can spread. That’s why it’s important to address the problem as soon as possible, or else the problem will only worsen.

How To Remove Mold From Inside The Toilet Tank

Drain The Water

Before you can remove mold from inside the toilet tank, you must drain the water. First, locate the water supply valve, which typically sits behind the toilet. Turn the valve to shut the supply off, then flush the toilet to drain the water.

Apply Vinegar

Fill the toilet tank with white vinegar. Some people fill the tank with a gallon, while others scrub the tank with a small amount of vinegar. Both are valid options, but you may have more luck simply pouring 1 cup of vinegar into the tank.

Use a toilet brush to move the vinegar around and scrub the mold in the tank. Ideally, you should wear a protective face mask to ensure you don’t inhale mold spores. If you don’t want to scrub the mold, you can pour a gallon of vinegar into the tank and let it sit for 12 hours.

Use Bleach

Some people prefer using bleach to treat their toilet tanks for mold, and that’s understandable. After all, bleach is quite strong, and mold is no match for it. Shut the water supply valve off and flush the toilet as described in the last step. Next, mix 1 cup of bleach with 1 gallon of water in a bucket, and pour it into the toilet tank. Let the mixture sit for 15 minutes, then scrub the mold. Be as thorough as possible, flush the toilet, and repeat the process as needed.

Summing It Up

Mold grows in a toilet tank because of the darkness and stagnant water. This problem is more common for people who don’t clean their toilet tank as often as they clean their toilet bowl. You can prevent mold from growing in your toilet tank by regularly cleaning it and improving your bathroom’s ventilation.

Related Guides:

• 9 Types of Toilet Flush Systems
• How To Unclog A Toilet With Poop In It (8 Ways To Do It)
• Standard Toilet Flange Dimensions (with Pictures)