ok first off root rot begins 80+ not 71+. How big is the container you are doing grow in?? Depending on container size you could take empty soda bottles (16oz, 20oz, 2l) fill with water then freeze. Place frozen bottle in rez and temps go down. Have about 4-6 bottles made up and in freezer that way when one is thawed just pop it back into freezer and grab another. If container that plants are in is a dark color then paint white to reflect some heat off container. :thumbsup: