I totally agree with the above advice. I've switched over to using this media in all of my five humidors and they all hold right around 65%, give or take.
You might need more media for the size humidor you're using. Go easy on the water at first, it takes very little to get these things going. Your cigars might be really dry to start with too, who knows. Try adding some more media and watch it slowly to see if the RH goes up (give it a few days).
Hope this helps.