Keeping the root zone temperature in a hydroponic garden at 20C or less while the air temperature is 24C or higher will allow for maximum growth of plants in the system. This slight temperature offset also helps keep plant health problems to a minimum. To accomplish this, keep the water reservoir at a temperature slightly below the desired root temperature with a do-it-yourself water chiller. Adjusting the water temperature with DIY chillers will depend on the size of the hydroponic layout and other factors. There are several DIY methods to chill a hydroponic water supply; when used in conjunction with one another it is easy to find an inexpensive solution that works well with any particular system.
Use an external water pump when pumping nutrients or water in a hydroponic system. The use of traditional submersible pumps will add heat to the water, thus increasing the water cooling required. For outdoor systems, replace a smaller water reservoir with a larger one. Smaller reservoirs heat up faster than larger ones because they do not require as big a temperature change to begin warming the water.
Top off the reservoir supply with cold water. When using tap water, always wait until the water begins to run cool, meaning that the water has not been heated by remaining inside the home's water pipes. The water will run from the tap at below 22C once water from the underground pipes supplying your home begins to reach the tap.
Keep a supply of frozen plastic 4 litre milk containers or other plastic drink bottles filled with water. Put the lids on tightly and fill the bottles 90 per cent full. Add a frozen bottle or bottles to your reservoir in the desired quantity to bring the temperature down to the level desired and replace as necessary.
Move the reservoir to a cooler room if indoors and place it on a cold floor or a concrete block to help draw the heat away from the tank through the floor or the block.
Use a fan to blow air horizontally across the top of the reservoir to aid in heat removal. Be sure the tank is kept full to achieve maximum cooling with this method, since evaporation will be greatly enhanced. If necessary, add a float valve to the tank so it will automatically refill the tank as the water evaporates.
Use a small portable air conditioner in the room where the reservoir is kept to keep the temperature of the room at the desired reservoir temperature. This method usually requires the air conditioner be turned on and off as necessary to avoid wasting electricity.
Use a cooling coil made from stainless steel immersed in the reservoir. The inlet end of the coil should have a hose adaptor on it that runs from a water supply on a tap that is turned on to a trickle. The outlet end also should have a hose to drain the water from the coil and into a drain or elsewhere where it could be used again. Use a small circulation pump in the reservoir to stir the water so that it moves over the cooling coil. The water running through the coil will pick up any heat and transfer it to the outlet hose.
The optimum temperature for most plants' root zones is around 20C. When conditions are too cold or too warm, plant growth will be stunted. Increased root death will occur under these conditions.