What is pH?
The unit of measure of nutrient solution acidity or alkalinity is termed "pH". It is a description of the concentration of the H+ ions in the feed solution, substrate or drain water.
The mathematical description is:
pH = -log10[H+] = log10 1/[H+]
This equation tells us that as the concentration of H+ ions What is in a solution increases, the more acid is the solution. Conversely, as the H+ concentration decreases, the more basic the solution becomes.
To control the pH and still retain a certain degree of buffering, the bicarbonate (HCO3) content of the raw water (bore-hole, well or mains) must be determined and adjusted to contain 40 to 60 ppm using one or a combination of acids. The naturally occurring bicarbonate ions in the water act as insurance against wide fluctuations in the pH of the solution. However some sources of water, particularly rainwater contain very little, if any bicarbonate (<6.1 ppm). Feed solutions composed of mainly rainwater will cause the slab solution to have an unstable pH. The addition of potassium bicarbonate to the stock tank will provide some buffering capacity under these situations.
The bicarbonate content of the water and the pH of the water are closely correlated. However, the pH is not a measure of the bicarbonate content in the water and the bicarbonate content is not a measure of the pH of the water.
The pH of the water will rise through the addition of bicarbonate ions due to its reaction with free hydrogen (H+). This will result in the creation of water (H2O) and carbon dioxide (CO2). More importantly however, hydrogen ions, which are what is measured by the pH meter, are removed from the solution. As a result, the pH meter detects fewer hydrogen ions and produces a reading indicating a higher pH.
