Temperature of the nutrient solution should be in the range of 65 to 80 degrees Fahrenheit (18 to 26 degrees Celsius). Before adding water to your reservoir, it is a good idea to allow it to come to the same temperature as the water in the reservoir. Plants do not like rapid temperature changes, especially in the root zone. Aquarium heaters can be used to warm the nutrient solution in the winter, and look for “chillers” to cool the solution in the summer if high temperature becomes a problem.