You could try a little fungicide on it. I don't think it would hurt it any. There are several types available (Cleary's, Mancozeb, etc.). You can mix it up and put it in a spray bottle and mist it on. If your plants are out in the open, I wouldn't think stagnant air is the problem unless the room they're in is closed and very hot. Usually that is more a terrarium issue.
Since I haven't had mold issues with mine (they are all outdoors), I can't offer any thoughts on the black spots. I have only seen my traps die off naturally.
Sounds like you are doing everything right though. You could try supplementing their light with a flourescent fixture (you can get small ones).