There are a lots of alternatives to help you solve your problem -- search is your friend. Just search this thread for humidity problems.
In a nutshell, as others have said a sponges are not good for managing humidity (RH). You can use
Boveda packets or beads (
Heartfelt, or
HCM) and your problems in all likelihood go away.
You should also take the time to
test and calibrate your hygrometer.
You should also go to the
New Inmate Thread and introduce yourself.