What is a musty odor in a terrarium can be elminated by adding?

A musty odor in a terrarium can often be eliminated by adding activated carbon or charcoal, which helps absorb odors and impurities. Additionally, ensuring proper ventilation and improving drainage can reduce humidity levels, preventing mold and mildew growth that contribute to the musty smell. Regular maintenance, such as removing decaying plant material, is also essential to keep the environment fresh.