Tips for controlling solution temperature:
In winter: Put a heat mat under your reservoir and/or use aquarium heaters for your nutrient.
In summer: Use chillers.
Protect your solution from direct sunlight: Insulate it or sink your reservoir in the ground.
If you can’t prevent temperatures from rising too high: Lower plant stress levels by lowering the strength of your nutrient solution.
A warm, dry environment evaporates water quickly: Evaporation can cause big problems by increasing the concentration/conductivity of the nutrient solution.
Can’t easily lower the temperature of your growing environment? Try covering your reservoir with black-and-white plastic (white side up, black side down). This will reflect light away and help prevent evaporation.
Reducing direct light on the solution will also slow or prevent the growth of algae and bacteria: If you’re growing indoors, be aware of the heat from plant lamps. A slight change in a light’s position can make a big difference to growth. Outdoors, or in a greenhouse, the amount of sunlight will affect the temperature of your growing environment.