And THIS is why I always advise against restricting airflow!

Actually, a little bit of mold isn't a big deal -- you can spot-clean it pretty easily. It's when you get
two-inch-tall mushrooms that you need to do an overhaul.
Also, if you still notice your top layers never drying out, it's possible you're adding too much water. Your substrate should be cool to the touch and not drip when you squeeze a handful of it. (The bottommost layers might right when you add it, but the water should wick up and distribute evenly within a few minutes.)
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