how often should i change the substrate. i have a rosie who likes his enclosure nice and dry and an a. avic. who gets a good deal of spritzing every couple of days. i dont see any fungus or mites or any crap like that. i give them fresh water every three days. and they are both well ventilated. just curious since these are my first t's and alot of the scientific folk have differing oppions. :? 