Krieg:what kind of hydrometer are you using? Could be your hydrometer, when was the last time you calibrated it?
urbino:You could buy a dehumidifier and put it in the room with the humi.
jihiggs: "Just the el cheapo one that came with my equally el cheapo Thompson humi." this is your problem, the dial style hygrometers flat dont work.
Marcos El Malo:I've never tried this in my humi, but you might try uncooked rice or salt crackers to absorb excess moisture. You might notice in high humidity locations that restaurants put uncooked rice in their salt shakers. As I said, I've never actually done this, and I have no idea what the physical parameters of uncooked rice might be., i.e., how much moisture they will absorb and at what temperatures. But I think this is what I'd do if I was trying to lower the humidity in my humi and the RH outside of the humi was higher than my target.