I have always used coconut husk and never had a problem! Never had mold! You must have moistened it too much! I buy the blocks and add water then let it dry out for a day or two then use it. I can get the blocks for $2 and it does my 20 long tanks no problem! The blcoks keep the water in it for weeks before humidity drops! The bags cost more and does less! Either one is great for bedding!