pH vs. Temp
Too often the dynamics of pH are not fully explained as an integrated system consisting of two primary parts: temperature and hydrogen ions. The best explanation of the interaction of pH and temperature: All water solutions of acids and bases owe their chemical activity to there relative hydrogen and hydroxyl ion concentration. In pure water, the equilibrium product of the hydrogen and hydroxyl ion concentrations is a constant 7.0 at 22 C. (71.6 degrees). Pure water is neither acidic nor basic. It is essential to recognize that pH measures only the concentration of hydrogen ions actually dissociated in solution and not the total acidity or alkalinity, a fact which accounts for the observed pH change in pure water with temperature variations. As the temperature of pure water increases, the amount of dissociation increases and the quantity of hydrogen and hydroxyl ions increase equally. Since pH is relative to the concentration of only hydrogen ions, the pH of pure water will actually decrease as the temperature of the water increases, although the water is still neutral. Therefore, unless the relationship between the dissociation constant and the temperature is known, it is not possible to obtain an accurate pH reading without compensating for temperature. Temperature fluctuations in a hydroponic solution seriously affect the solubility of nutrients. Each inorganic mineral has a precise temperature range for maximum solubility. Studies show that the ideal water temperature for total solubility of plant nutrient formulas is within the range of 68-72 degrees (20-22 C.). When temperatures are higher or lower than this ideal, insolubility occurs with many of the trace elements. Temperature outside the ideal range have the same effect on plants that a pH above 7.5 has --- iron, manganese, copper, zinc and boron become less available to plants. The solubility of phosphorus acid, calcium, and magnesium is sharply reduced when the pH of a nutrient solution drops below 6.0 and the solubility of toxic substances, such as soluble aluminum and excessive iron compounds found in tap water, is greatly increased.
