Your plants’ growth will be slowed down if the temperature of your nutrition solution is too low. Root infections like pythium will be encouraged if the solution becomes too warm. Moreover, water can store less dissolved oxygen the warmer it gets. The optimal range for nutrient solution temperature is roughly 18°C to 20°C (65F – 68F). To maintain the proper temperature range in your hydroponic tank throughout the winter, you might need to install a water heater. A water cooler can assist maintain the roots healthy and happy with plenty of dissolved oxygen during the summer because the reservoir temperature might soar (especially with hot grow lamps on in the room).