I switched to cyprus mulch and havent had the issue since.. another good one is coco husk.. it comes in a brick that you have to soak but it only costs a fraction of cyprus mulch..
also a plexi lid is a great solution to humidity issues.. I made a post on how to make one a while back.. let me link it to you.
http://ball-pythons.net/forums/showt...ng-a-plexi-lid