Musty cage smell?

[Aanayab1]

My monitor cage stays 75% or better humidity with no visible mildew/mold but it sure smells of it. My only concern is the risk of possible respitory issues, if there even is one. Little guys are growing like beasts and have crazy amounts of burrows. They have a nonstop food supply litteraly. I see all all 4 eat daily and almost everytime I look in cage at least one is eating. I do not see any signs of illness. I'm only asking about the possible issues because I randomly thought of it. Thanks in advance for any opinions or information.

[infernalis]

Is it warm enough out to gather some leaves??

Leaf litter from a forest will boost your bacteria count and help freshen up the inside of the cage.

scattering about an inch of fresh dirt on top helps too.

I can't see any health issues from a musty smell, I can only imagine how musty the air has to be down deep in a dank burrow.