After trying almost everything I can think of I still cant get my cool end temp up. It sits at between 73-75. I know that its too cool but I dont know what to do. My warm end is at 90. I have a 20g long tank with a screen top with aluminum foil covering part of it. I have a 12"x11" peice of flexwatt connected to a Zoo Med 500R thermastat. I an extra peice of flexwatt. Please help. I know that the low temp isn't healthy.