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A major reason growers opt for water culture systems is that the growth and maturity rate is generally 15-25 per cent faster. Growers can still get their desired plant size with a shortened vegetative period. So, to get the anticipated optimum production from these systems, using the proper mix of nutrients and having the right conditions is that much more important.
The temperature and absence of light in the water, as well as the general cleanliness of the tank, feed lines, and pump, will have major impacts on just how long a system can go between rinsing and cleaning. Typically, between one and three weeks is the range that seems to work best. If growers change the water more often than necessary, their workload and nutrient costs go up. If they change it too seldom, the likelihood of increased harmful microorganisms and plugged up system components can go up. Finding the balance is important for every grower. Healthy plants require good nutrition and they are much more likely to put off the chemicals from plant allelopathy, which fight off competition from other parasitic plant life forms.
With soil systems, the intent is to create healthy and plentiful living and beneficial microbes to assist the root systems in uptaking nutrients. However, much of the organic food that builds healthy microbe populations will also support many undesired bacteria and fungi. As such, many water culture growers prefer to use ionic nutrients. These are the nutrient salts that beneficial microbes create when they react with organic non-ionic nutrients. This lack of a food source will aid in keeping harmful microbe populations from developing. The other side, fungi-like mycorrhizae, which are still very beneficial for deep water culture crops, will also not have any support to develop and grow.
If growers decide to use organic nutrients in a deep water system, it is recommended they make routine changes. Growers should also clean the solution, keep light from entering the water reservoirs and channels, and keep the oxygenation of the water at its maximum.
Though not generally considered a plant nutrient, oxygen is a primary nutrient required for use by the root system. A lack of oxygen can aid in the development of anaerobic bacteria, which is undesirable. A couple teaspoons of three per cent hydrogen peroxide per gallon of water in your system can be a great nutrient addition for a deep water system. This extra oxygen will help the roots to better absorb nutrients and reduce the spread and growth of harmful microbes. Just add this a few hours before adding other nutrients so it can stabilize properly.
Liquid nutrient temperature is also very important in water culture systems. The best range is 62-68°F. When the temperature gets above 72°F, the dissolved oxygen will drop. When the temperature gets below 60°F, it affects plant metabolism and can change the state of growth.
Another aspect that has a major impact on the uptake of many nutrients and needs to be carefully monitored is pH. Because there is little buffering capacity when deep water systems are filled, there are subsequently small microbial populations or organic material to be converted—usually only what the grower has added. The new water is usually low in total alkalinity, which doesn’t help stabilize pH. With the use of a total alkalinity buffering product (pH up), the pH of the solution will tend to be much more stable and hence plant uptake will be improved, causing plant health and production to increase accordingly. Nutrient buffering solutions have been developed with the addition of agents like potassium carbonate that not only increase total alkalinity (total alkalinity is the measurement of the amount of acid required to bring a solution down to a pH of 4.1), but also increase the pH. So, if not compensated for, these nutrient buffering solutions may then make pH too high. The acids needed to then bring the pH back into the proper range will be found in products called pH down. By using pH up and pH down products together, growers can achieve the desired pH while also creating a more stable solution through higher total alkalinity. Usually the desirable balance range for total alkalinity will be around 50-75 ppm of calcium carbonate. There are inexpensive test kits for measuring total alkalinity. Overall, the goal is to establish a more stable water profile while keeping the pH within the proper range (this varies for different plants but is often between 6 and 6.5). The superior hydroponic practice is to get to a stable total alkalinity and pH range quickly and then maintain that through moderate use of the needed buffering solution. Of course, your influent water may already be within a stable range for pH control.
In water culture hydroponics, there are a number of differences from other forms of indoor and hydroponic systems. Cleaning, testing, adding nutrients, and making adjustments are more critical, but the rewards are definitely there in the end. Hence why so many commercial grow operations utilize these systems and maximizing yield is top of their list
Source: Maximum Yield May 2 2018 "Making the Most of Hydro Nutrients" https://www.maximumyield.com/making-the-most-of-hydro-nutrients/2/3887