Symptoms
- Pink, black, or greenish slime inside the tank
- Musty smell from the mist
- Slippery film on the tank walls
- Buildup returns quickly after cleaning
Likely causes
- CommonWater left standing in the tank for multiple daysStagnant water is an ideal environment for mold and bacteria to grow.
- CommonTank not cleaned regularlyEven with fresh water added on top, residue from previous fills builds up over time.
- PossibleHumidifier stored wet between usesA damp tank left closed up between seasons is a common source of buildup.
What to do
- Empty the tank completely and wash it with warm water and a small amount of dish soap, scrubbing all interior surfaces including corners.
- Disinfect by filling the tank with a solution of one teaspoon of unscented household bleach per gallon of water (or diluted white vinegar) and letting it sit for 20–30 minutes, then rinse very thoroughly multiple times.
- Clean the base and any water-contact parts the same way, making sure no cleaning solution residue remains before refilling.
- Empty and refill the tank with fresh water daily, and do a full clean at least once or twice a week.
- Let all parts air dry completely before reassembling and storing.
- Use distilled water and change it daily going forward to slow future buildup.
Tools and parts
- Dish soap
- Unscented household bleach or white vinegar
- Bottle brush
When to call a pro
No professional needed for cleaning; replace the unit if mold keeps returning quickly even with regular cleaning and fresh water.
Safety
Use caution
Never mix bleach with vinegar or other cleaners, rinse the tank thoroughly after disinfecting, and ensure good ventilation while cleaning.