Yup, I found good info with a web search for "white mold on soil"
"White mold is a saprophytic fungus frequently found growing on the soil and other areas such as wood-based surfaces. It is the most common of all mold types and can be identifiable by its white fuzzy look on the surface of your soil. "
Ever noticed any white, fuzzy appearance or brown powdery mildew on the surface of your houseplant soil? It is a clear indication that you have mold on the soil.
You got it! My lower fan wasn't working in addition to high humidity and a couple other things.
I'm doing DTW coco for the first time, it settled more than I expected and left the top of the coco recessed down in the pot almost 2 inches and the foliage almost capping it off. I added more coco into the bottom of the pot so the coco is now about even with the top, more room for airflow. I might also increase the time between fertigations. And do some defol on the bottom.