Mold in Your Water Softener: How to Spot it and Stop it

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The whole purpose of a water softener is to improve your water quality, so finding mold in your water softener is alarming.

Don’t panic, though – mold is usually easy to get rid of and you can often prevent mold from returning in the future.

Here, we’ve shared everything you need to know about mold in a water softener resin or brine tank.

📌 Key Takeaways:

  • Mold in water softeners is caused by a combination of oxygen, organic matter, and moisture.
  • Mold is most likely to be found in brine tanks, but could also accumulate in the resin beads.
  • To remove mold from the brine tank, use a wet vacuum to suck out the water, then remove the salt (including any salt bridges) and scrub the tank with soapy, warm water.

🧫 What Causes Mold In Water Softener?

Mold is most commonly found in a water softener brine tank.

Your water softener’s resin tank may also accumulate mold, but this may go unnoticed as you don’t routinely look inside this tank and the narrow opening makes it difficult to see into the resin.

The cause of mold in your water softener is the organic substances in your water, which combine with the oxygen in your tank to form colonies.

Mold thrives in moist environments, and it’s more likely to grow if your water softener is installed in a location with a high humidity level and condensation.

Mold in water softener brine tank

⚗️ Is Mold In A Water Softening System Dangerous?

Yes, mold in your water softener can be dangerous.

If the mold comes into contact with water in the system, mold spores could dissolve into your water supply. Drinking water containing mold may have adverse health effects, including nasal and throat irritation, headaches, sickness, and respiratory problems.

Mold in your water softener system could also spread to other water-using appliances downstream in your plumbing system, leading to costly repairs and replacements.

🆚 Mold Vs Dirt In Brine Tank

If you see dark stains on the inner walls of your water softener brine tank, you might immediately conclude that you have a mold problem.

However, the more likely cause of this dark-colored staining is dirt and impurities from the softener salt.

Even high-purity softener salt products contain some dirt. This gets left behind in the brine tank when salt dissolves in the water.

This dirt accumulates on the walls of the tank, eventually becoming noticeable.

👨‍🔧 You can remove the dirt by cleaning the tank regularly. Reduce the accumulation of dirt by buying a high-purity softener salt, like evaporated salt.

❇️ How To Get Rid Of Mold In A Water Softener

The best way to get rid of mold in a water softener is to establish a water softener maintenance schedule – and stick to it.

The more often you clean your water softener, the less likely that mold is to accumulate.

Clean The Brine Tank

You should clean your brine tank every 1-2 years, depending on the quality of your salt, your water usage, and your water hardness. Physically scrubbing the walls of the salt tank is the best way to get rid of debris that has accumulated, including mold.

To clean your water softener brine tank, follow these steps:

  1. Wait for the salt level to get low, then shut off your water
  2. Drain the water softener tank by vacuuming or scooping out the water
  3. Scoop out the remaining salt with a shovel or a bucket
  4. Rinse out the tank and scrub the sides with detergent to remove any buildup
  5. Set a manual regeneration cycle
  6. Add a fresh batch of water softener salt to the tank

👨‍🔧 You can use a diluted household bleach solution in place of detergent if the staining in the brine tank is heavy. Just make sure to take safety measures, including wearing rubber gloves and airing the room by opening the windows, during cleaning.

US water light duty twin brine tank

Use A Resin Cleaner

Cleaning the resin will get rid of any mold that might have accumulated in the resin tank. Buy a resin bed cleaner and use it once or twice a year in the water softener system.

Resin cleaners are designed to remove impurities that aren’t easily flushed out of the resin during a regeneration cycle, including iron stains, sediment, and mold.

Due to the design of the resin tank, you’ll struggle to physically clean the inside walls of the water softening resin tank. However, a resin cleaner should flush out the entire tank and lift mold from all surfaces if present.

Run A Bleach Cycle

If you want to clean the whole water softener at once, you can program the softener to perform a “bleach cycle”. Before you start, check your user manual to make sure it’s safe to use bleach in your water softener tank.

Some softeners have a special setting for running the black cycle. Switch this setting on to get started.

Then, follow these steps:

  1. Prepare the bleach. A 9-inch brine tank needs 1 cup of bleach, and a 12-inch tank needs 2 cups of bleach.
  2. Close the brine tank lid and set the system to perform a manual regeneration.
  3. Wait for the regeneration cycle to finish. This will remove all bleach water from the whole system.

This method is a good way to sanitize your water softener, but it won’t eliminate the black stuff from your water softener tank.

For that reason, it should be used to supplement the above water softener maintenance tasks, but it shouldn’t be used alone for mold removal.

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🚫 How To Prevent Mold Growth In Water Softening System

There are several different ways to reduce the likelihood of mold in water softeners:

Install The Softener In A Low-Humidity Location

If mold growth is present in various spots around your home, you’ll know just how challenging it can be to prevent.

In many cases, preventing mold requires you to take steps to reduce humidity and increase airflow as much as possible throughout your home.

You’ll only be able to eliminate mold growth in your water softener tank if you take away the environmental factors that allow mold to grow.

This could mean installing your water softener system in a room that has low humidity and no condensation, or setting up a dehumidifier in the room near the water softening system.

Increase The Softener’s Regeneration Frequency

Water softeners need to regenerate frequently to circulate water through the system and prevent a buildup of mold and bacteria in the resin and brine tank.

If your water softener gets moldy and you don’t have any humidity or moisture issues in your home, you might need to schedule more frequent system regenerations.

👨‍🔧 It’s recommended to set your water softener to regenerate around once every 7 days, depending on your water usage and quality, and the size of the water softening system.

US water light duty twin head valve

Change The Sediment Filter

Most water softeners come with a sediment pre-filter, which protects the softening resin from contamination.

Sediment filters last for about 3-6 months. They should be replaced frequently to prevent clogging, which could reduce water flow and allow trapped contaminants to re-enter the water supply.

An old sediment filter might also accumulate mold, and mold spores may split off and travel into the water softener’s resin or brine tank.

If your water softener doesn’t even have a sediment filter, install one! It’ll protect the resin from dirt and reduce the organic matter responsible for mold growth.


What is the black stuff in my water softener?

The black stuff in your water softener brine tank could be several things, including mold or debris from your water softener salt pellets. If you house your softener in a humid location, it’s likely that the black deposits are mold.

How do I get rid of mold in water softeners?

The best way to get rid of mold in water softeners is to empty out and clean the brine tank. You could also use a resin cleaner to prevent a buildup of mold in the resin beads, and sanitize the softener with a bleach solution.

How do you clean the inside of a salt tank?

To clean the inside of a salt tank, wait for the salt level to drop, then use a wet vacuum to such out the water and scoop out the remaining salt with a shovel or bucket. Clean the inside of the brine tank and brine reservoir. Use soapy water and a sponge, or, for heavy soiling, diluted bleach. Rinse the tank thoroughly with clean tap water, then carry out a salt refill and program the softener to perform a manual regeneration cycle.

Can bacteria grow in a water softener?

Yes, bacteria can grow in a water softener. This is especially likely if the softener regeneration process isn’t frequent enough, or the softener is installed in a warm, humid location. Bacteria growth in water softener tanks isn’t always dangerous – many bacteria in the environment are harmless to humans.

  • Jennifer Byrd
    Water Treatment Specialist

    For 20+ years, Jennifer has championed clean water. From navigating operations to leading sales, she's tackled diverse industry challenges. Now, at Redbird Water, she crafts personalized solutions for homes, businesses, and factories. A past Chamber President and industry advocate, Jennifer leverages her expertise in cutting-edge filtration and custom design to transform water concerns into crystal-clear solutions.

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