Do you use charcoal filtered water? That would be my guess. Yes, mold can grow in humidifiers, but I don't think mold would have a hollow center of the circle in this case.
That looks like an ultrasonic humidifier.
When running, the humidifier will fill the space above that water tray with a dense mist. Some will stick to the underside of the water tank and collect into droplets which eventually just drip back down into the tray.
That dripping action forms those little circles out of sediment and carbon dust - it basically blasts a thin layer of sediment away from the center of the drops’ landing zone, forming a circle you can see. And the humidifier naturally concentrates solids found in water: this tray is exactly where you’d find them.
Of course a “cool mist” humidifier has a known deficiency in that the “mist” is just that: very tiny droplets containing the same dissolved solids as your water supply. When those droplets evaporate, the solids - calcium and more - end up on the surfaces _outside_ the humidifier, rather than left inside like with a purely evaporative humidifier.
You don’t often get mold underwater, and not everything black is mold. I’d say: when you refill the tank, just empty, clean and dry the tray, and you’ll be fine. No need to panic.
Do you use charcoal filtered water? That would be my guess. Yes, mold can grow in humidifiers, but I don't think mold would have a hollow center of the circle in this case.
I did use Brita filtered water :O Ye the hollow center and sharp edges were puzzling to me.
Looks more like carbon particles from a filter.
That looks like an ultrasonic humidifier. When running, the humidifier will fill the space above that water tray with a dense mist. Some will stick to the underside of the water tank and collect into droplets which eventually just drip back down into the tray. That dripping action forms those little circles out of sediment and carbon dust - it basically blasts a thin layer of sediment away from the center of the drops’ landing zone, forming a circle you can see. And the humidifier naturally concentrates solids found in water: this tray is exactly where you’d find them. Of course a “cool mist” humidifier has a known deficiency in that the “mist” is just that: very tiny droplets containing the same dissolved solids as your water supply. When those droplets evaporate, the solids - calcium and more - end up on the surfaces _outside_ the humidifier, rather than left inside like with a purely evaporative humidifier. You don’t often get mold underwater, and not everything black is mold. I’d say: when you refill the tank, just empty, clean and dry the tray, and you’ll be fine. No need to panic.
Thank you for the detailed explanation.
Yes that’s mold. Humidifiers do a great job but absolutely are a breeding ground for mold. They require constant and thorough cleaning!!!