Why is maintaining a stable pH so difficult?
Three major factors tend to disrupt the stability of the pH in any hydroponic system. Learning to control these influences is essential for a successful harvest.
pH imperfection #1: the pH of the water used to dilute nutrients
Freshly distilled or deionized water has a pH of 7. However, the pH of the water may fall to as low as 5.5 within hours of preparation. This is because water absorbs carbon dioxide (CO2) from the air.
The behavior of tap water is even more complex. It contains dissolved and slightly alkaline calcium and/or magnesium salts. In this case, absorption of CO2 from the air makes predicting the pH even more challenging.
Because the calcium and magnesium salts in most tap waters, not to mention even more chemically complex well and spring waters, create such serious problems, many hydroponic growers, from hobbyists to huge commercial greenhouses, prefer using treated water. Although a number of water treatment systems exist, reverse-osmosis (RO) is considered the most economical. Water obtained from an RO system is almost as good as expensive distilled water.
Another option is to adjust the pH of tap water before using it. This can be done with so-called pH up or pH down additives. However, this task is demanding and often done incorrectly-and what's worse, the acidic and alkaline chemicals used in these products, and the resulting sudden fluctuations in pH when they are added to the reservoir, can be hard on your plants.
pH imperfection #2: biochemical processes in the nutrient solution
Many pH changes are caused by the nutrients themselves.
The more compounds in the water-measured in parts per million (ppm) or by the nutrient solution's electroconductivity (EC)-the greater their influence on pH.
For example, the urea used in many fertilizers is broken down by enzymes into one molecule of CO2 (a slightly acidic compound) and two molecules of ammonia (a slightly alkaline compound). This can cause erratic changes in pH.
In addition to urea, any compound containing an amide chemical bond (e.g., the proteinates used in many fertilizers) can, when broken down, affect the pH in unpredictable ways.
Nutrient absorption also leads to changes in pH. When a plant absorbs a lot of potassium ions, it gives out hydrogen ions in return. The result is a net decrease in pH. The situation reverses when the plant absorbs a lot of nitrate ions and gives out hydroxyl ions to compensate, thus increasing the pH (Bar-Yosef, Ganmore-Neumann, Imas, and Kafkafi, 1997; Ryan, P.R. and Delhaize, E., 2001). The higher the rate of nutrient absorption, the more dramatic the change in pH.
pH imperfection #3: the substrate through which the nutrient solution flows
The growing medium (also called the substrate) affects pH as well. For example, coco-based growing media undergo subtle changes during your crop's life cycle that affect the pH of the nutrient solution. Even baked clay pellets, which are far more stable than coco coir in terms of pH, are less than rock solid in this regard.
In fact, every chemical or biochemical process that goes on in the growing vessel changes the pH of the nutrient solution. Each additional factor drives it further from the sweet spot.
In nature, the volume of surrounding soil-teeming with microbes, humates, and other pH stabilizing agents-does a good job of offsetting pH changes. Natural soils thus act as natural pH buffers. That's why, in outdoor gardens, where the soil itself contributes to a more stable pH, changes in pH are more gradual than in a hydroponic gardens.[SUP]1[/SUP]
In hydroponics, however, pH stability is a challenge. It is an intense gardening method where the concentration of nutrients and their absorption rate by plants are much higher than in soil. As a result, chemical and biochemical processes influence the pH to a much higher degree than in natural soils or traditional agriculture. The natural stabilizers and buffers in the nutrient solution, mainly phosphates, are weak, so indoor gardeners have to check the pH of the nutrient solution regularly and adjust it when it goes below or above the sweet spot. What a hassle.
Stabilizers and buffers: the secret to pH balance
As already mentioned, in biochemistry, including agrochemistry, the pH of the nutrient solution and growing medium is balanced and maintained by stabilizing and buffering agents. But which stabilizers and buffers, and how much, are needed? Unfortunately, there is no easy answer.
Every pH stabilizer and buffer has its own optimal pH range where it works best. For example, phosphate stabilizes the pH in the area of 7.2. Other ions with buffering properties which are present in conventional nutrient systems are even less effective at stabilizing the pH near the sweet spot.
So, growers need guardrails of sorts along the nutrient highway to ensure that after the initial reaction that adjusts the pH within the sweet spot, it stays locked within that range. In this way, the pH will not be allowed to drift too far one way or the other along the pH scale. This serves as a kind of failsafe mechanism, providing you with further peace of mind while safeguarding your valuable crops.
The task assigned to the scientists at Advanced Nutrients was to research every available option for stabilizing and buffering the pH of the nutrient solution and growing medium. They were asked to develop a pH stabilizer and buffer that worked well in maintaining the pH within the sweet spot without an excessive amount of acids or alkalis.
One problem they encountered was the fact that every pH stabilizing agent has a limited pH-balancing capacity. For example, a weak stabilizer or buffer can handle only minor deviations from the optimal range caused by a small amount of acids or alkalis. By contrast, a strong stabilizer or buffer, with a large pH-balancing capacity, can keep the pH equalized even when large amounts of acids or alkalis are present in the nutrient solution.
Unfortunately, pH stabilizers and buffers cannot be strengthened at will in hydroponics. Cultivating crops involves more than pure chemistry.
Another factor is cost. Sophisticated stabilizers and buffers having all the desired properties, including low plant toxicity, are costly. Therefore, increasing their concentration can make a fertilizer prohibitively expensive.
More serious problems arise when plant biology comes into play.
For example, the optimal pH inside a plant's tissues is higher than outside the plant-generally in the range of pH 7.2–7.5. Fortunately, plants have their own mechanisms that keep the pH within this range. But by adding only a small portion of the wrong external pH stabilizer or buffer, you can destroy your plants' internal pH-balancing system. The result is damage or even death to the plant.
Yet another problem arises when looking at your plants' microscopic root tips. These fragile tips pump hydrogen ions into their immediate vicinity to make the pH more acidic. Here the pH can drop to as low as 4. This acidic pH level exists just around the tips. However, it is crucial for overall development and growth of root mass (Nye, 1981). Adding too much pH stabilizer or buffer can destroy the ability of these tender root tips to create the desired acidic micro-environment. If that happens, overall root development will be slowed, resulting in poor yield.
http://www.advancednutrients.com/breakthrough/
