Getting rid of mold/mildew in a humidifier that has sat for months in a basement

Anyone have experience with this?

I left a small amount of water in a sonic humidifier after I harvested my last grow, and left it in the basement for 6~ months, just yesterday I went to go grab it to clean and start up again, and I found a LOT of round little white mold/mildew dots or colonies covering the inside of the tank.

What would you use to clean this? Would you replace it?
I don't want spores becoming airborne via me not cleaning it properly.

Honestly am leaning towards replacing just to save a headache, but what do you guys think?