What about nutrient solution temperature?
The hydroponic nutrient solution is not just a mix of fertilizer salts and water, there are a number of organisms and compounds commonly found in our hydroponic systems that we need to be aware of. One of the most important of these is dissolved oxygen, which is vital for the health and strength of the root system as well as being necessary for nutrient uptake. Most growers are familiar with the need to have some form of aeration in their nutrient solution – whether they be in a recirculation or a media based system. In NFT systems, this is often accomplished with the use of an air pump or by allowing the nutrient to fall back into the reservoir, thus introducing oxygen. However, the effect of temperature of the solution on the dissolved oxygen levels and on root respiration rates also needs to be taken into account. As the temperature of your nutrient solution increases, the ability of that solution to ‘hold’ dissolved oxygen decreases. For example, the oxygen content of a fully aerated solution at 10°C (50° F) is about 13ppm, but as the solution warms up to 20° C (68° F) the ability of the liquid to ‘hold’ oxygen drops to 9 – 10ppm, by the time the solution has reached 30° C (86° F), then it’s only 7ppm. While this may not seem like a huge drop in the amount of dissolved oxygen, we have to remember that as the temperature of the root system warms, the rate of respiration of the root tissue also increases and more oxygen is required by the plant. For example, the respiration rate of the roots will double for each 10°C rise in temperature up to 30°C (86° F). So the situation can develop where the solution temperature increases from 20° – 30° C (68° – 86° F) during the day, with a mature crop and a large root system, then the requirement for oxygen will double while the oxygen carrying capacity of the solution will drop by over 25%. This means that the dissolved oxygen in solution will be much more rapidly depleted and the plants can suffer from oxygen starvation for a period of time.
Nutrient Solution Temperature The temperature of a nutrient solution in a reservoir is one of the most important factors affecting the dissolved oxygen content of the solution. In fact, water's ability to hold oxygen is directly related to its temperature. As the temperature of the water (or the nutrient solution) gets warmer, the dissolved oxygen potential decreases. As the temperature of the water gets colder, the dissolved oxygen potential increases. Since oxygen is good for the plant's roots, a grower should try to have the coldest nutrient solution possible, right? Well, not exactly. If the temperature gets too cold, a whole new set of problems are created. Temperatures
that are too cold will cause the plant's growth to slow and eventually stop altogether. Most indoor horticulturists experience nutrient reservoir temperatures that are too warm. This causes a decreased dissolved oxygen content, which allows anaerobic pathogens to make their home. Pythium, or root rot, is the most common pathogen that plagues the indoor grow cannabis with warm nutrient reservoir temperatures. The optimal temperature for a nutrient reservoir is 63 to 72°F. Within this temperature range, the dissolved oxygen content is high and the temperature is warm enough to facilitate nutrient uptake.
Optimum Water/Nutrient Solution Temperatures The optimum Nutrient solution temperature may vary a little bit depending on who you ask and type of plant, but the optimum water temperature for your hydroponic systems is between 68 and 72 degrees Fahrenheit (20 to 22 Celsius). Some will increase that range a little bit to between 68 and 75 degrees Fahrenheit (20 to 24 Celsius). Either way there's not much difference. With that said, you don't need to worry if your nutrient solution temperature is slightly outside of that range. After all the term "optimum" is just referring to the most favorable conditions possible. If your nutrient solution/water temps are close to the optimum range, I wouldn't worry at all. You just don't want it to get too far outside of that range. You don't really need to start being concerned unless the water temperatures begin to reach 80 degrees Fahrenheit (27 Celsius). Or if it start dropping below 60 degrees Fahrenheit (16 Celsius).
Checking your Nutrient Solution Temperature Checking your reservoir temperature is really easy and simple to do, and you don't even need any expensive special equipment to do it. All you need is a small basic glass aquarium thermometer from anywhere that sells pet supplies. I get them at Wal-Mart for $2. Don't get the stick on kind that change colors, their not accurate enough. Make sure to get the glass ones with the small suction cup to stick on the inside wall of glass aquariums. I tie a string around the small suction cup and wrap the string around a empty plastic spice bottle I saved and cleaned out. That way I can store the glass thermometer inside the plastic bottle to keep it safe when I'm not using it. The string makes it easy to dunk and pull the thermometer back up out of the nutrient reservoir. Especially with my nutrient reservoirs that are in the ground. I don't have to lie down to reach in it, I just pull it back up with the string.
Hydroponic Nutrient Solution Temperature
If you were going to maintain a hydroponic nutrient solution at a steady temperature for the entire life cycle of the plant, from germination to harvest, 70-72°F/21-22°C is a good choice. But depending on conditions, altering the temperature might be more beneficial. For germinating, as well as seedlings and clones that haven't rooted, warmer temperatures are preferred. Aim for hydroponic nutrient solution maintained at temperatures between 70-75°F/21-24°C for faster growth while germinating and with seedlings or clones, until you can see new root growth. Some growers say they obtain better results at temperatures as high as 78°F/25°C for water or nutrient solution temperatures during these, the earliest stages of the life cycle. As you raise the temperature of the hydroponic nutrient solution, you provide an environment more favorable to bacteria, germs, mold, other things that can have a negative impact. It also reduces the amount of oxygen the nutrient solution can absorb. Warmer nutrient temperatures are generally better for germinating, seedlings, clones. But these early stages of growth are when the plants are most vulnerable to organisms that will attack them.