Cannot get humidity down..

I've had my humidor for over two weeks now, and I cannot seem to get my humidity down. I have a Savoy medium sized humidor with a sponge humidifier (that came with it). I have left it open for hours at a time, and the humidity is still reading around 74-76%. I am using my analog hydrometer as well as my digital hydrometer, both reading the same RH.

I cannot figure out what exactly to do. I don't want to leave it open too long and dry it out completely.

Does anyone know of a way to get this problem solved once and for all? Any input would be greatly appreciated.