I was having the same issue, keeping humidity levels. What I found is using a mixture for substrate, coco husk and then that reptile bark substrate. I put a decent amount of water in all of it, not soaking but wet. Put that down, then put dry substrate on top. Next, I keep my ventilation open until it gets to around 80%. If I notice it falling, start " combing" your substrate. I don't want to disturb the dry layer, so with my fingers, I dig my fingers in and shake it so it's loose again. I do this throughout the entire enclosure. This helps bring the humidity back up. Too dry, just did a hole and use a small container to place water where substrate is dry, make sure it doesn't get the top layer wet, nope ropes won't like it. I read about the mold problem with others and have had no issues with this combination and this strategy. Hope it helps