what kind of heat source do you have in there? i have heat mats under neath my tanks and never had any losses of any of my 7 species. mid tank is low 70's about 80 on the sub. surface about 110 on the bottom under the sub. the roaches just hang where its most comfortable for them. better than heating a room to one temp. in my opinion as they can get closer to the heat when cold further away when hot. room temp is 65f.