Wick Mold Question

[Firemedic]

I have been running an Astriocrat Set and Forget system, sine Late April. Keeps humidity set perfectly in my humidor at 69. However, I've noticed spots of mold starting about every thirty days of replacement. I'm currently on my third wick, and wondering if they should be replaced as soon as spots appear, or if they still have some life left. I only use distilled water, and clean the container every time I replace the water. I was told one cartridge should last me around three months.