Searching for the Cause of High Humidity in a Studio Aparment

[Brian Childres]

I'm stuck. I have 2 units (upstairs), 425 sq. ft. each, that recently have a relative humidity of around 72%. There are no leaks, no moisture anywhere, and we added several soffit vents. Also, the 18,000 BTU mini-splits are working fine for each unit, and it is 1985 construction, location is Tyler, TX. We discovered the humidity problem from one of the tenants seeing a small amount of green mold (this is a fairly new tenant). I have owned the 8-plex for a little over a year. Any thoughts besides installing a built-in dehumidifier? Thanks!