woke up this morning and there was fog on the cold side of the viv, i imediatly checked the temperature and it was 18 on the cold side and just 20 on the warm!!

ive now turned up the heat mat stat, and put in a heat bulb instead of the 85W day light bulb, i really dont want them to hybernate or anything, is there anything else i could do? anyone else ever had this problem? and also should i put another heat mat in on the cold side but keep it on only at night??? HELP PLEEASEEE!!??? XX thanks guys. X
