Keep your tank changes weekly or bi weekly 72 is fine. I'm running 73. Chiller isn't needed for 3 degrees. If your worried about it freeze a few 2L bottles of water. Change them out once or twice a day. But 60-69 is the best range. To cold and non purple buds can turn purple. My MK will stain your hands purple when I get under 60. But might do it this grow. Been ask for purp. Just haven't gotten seeds yet.