pH and Nutrition in Hydroponics

Water also is known as H20 because it has two hydrogen atoms and one oxygen atom for each water molecule. From this base molecule, it can accept an additional hydrogen ion to become H3O, and become acidic. It can also lose a hydrogen ion to become HO, and become basic (alkaline). The pH scale is a measure of whether water has additional hydrogen ions (lower on the scale, acidic), or is missing hydrogen ions (higher on the scale, basic).

Pure water has a pH of 7, and is the center point of the pH scale. It is neither an acid or a base.

Substances that have extra hydrogen ions to donate to the water, are known as acids. If you add an acid to water, it gives the water extra hydrogen ions, and the water becomes more acidic. The more extra hydrogen ions there are, the stronger the acid, and the lower the pH value. This is why if the nutrient solution tests too high of a pH, you can add General Hydroponics’ pH Down to lower pH. The acid in pH Down donates hydrogen ions.

Substances that will soak up and capture hydrogen ions from water are known as bases or alkalines. If you add a base to water, it will take away hydrogen ions from the water, and the water will become more basic. If the pH reading of a nutrient solution is too low, adding a base such as General Hydroponics’ pH Up to capture hydrogen ions and raise your pH.

Understanding pH Readings

Acids have a low pH, and bases have a high pH, pure water sits in the middle at 7. The lowest number on the pH scale is 0, which is a very strong acid, and the highest is 14, which is a very strong base.

The pH scale is logarithmic, not linear. Each full number difference is a factor of ten in difference. For example, pure water has a pH of 7, a pH of 6 is a 10 times stronger acid, and a pH of 5 is 100 times stronger.

To check the pH of your nutrient solution, either use a meter, or a General Hydroponics pH Test Kit. To use the test kit, fill the test vial halfway with the solution to be tested, and add 3-5 drops of the pH test indicator fluid. Cap the vial, and tap the side while holding lightly to mix. Compare the color of the liquid to the colors on the label. If the resulting fluid is yellow, the pH is around 6.0 and acceptable to use. Orange or red indicate low pH, add pH UP in increments of 1-2 ml per gallon, giving each treatment time to disperse before retesting. Green or blue indicates high pH, add pH Down as above to lower pH.

Since the test fluid is only used at a few drops at a time, the bottle that comes with the test kit lasts for many tests, and does not require batteries or calibration.

Source:General Hydroponics

Nutrients availability at different pH value

The pH value measures the ratio of H+ ions to OH-base ions in the soil. If the soil solution has more H+, the soil is acidic. If the OH-dominates, the soil is alkaline. The equal balance between them is neutral and its value 7.0. The soil pH value interacts with the mineral nutrients. Availability is determined by the soil pH and varies for each nutrient. High or low pH causes toxicity and decreases microbiological life in the soil.

Sodium raises pH and destroys soil structure. High pH makes elements such iron zinc and manganese less soluble. Low pH leads to continuous acidification in the soil. Acidification can be the result of the excessive use of fertiliser, or it can also occur naturally. For example, a mass of vegetation in a warm and moist condition during decomposition produces high quantities of carbon dioxide. In another instance, acidic  cations in large amounts replace the natural nutrients and cause acidity in the soil. Strong and extremely acidic soils are deficient in calcium and magnesium. Alkaline and strong alkaline soils contain high levels of free limes. Extremely alkaline soils are usually sodic soils. The positively charged sodium ions attract the negatively charged soil particles. The soil particles move close to each other, which creates a soil compaction. As a result, the water infiltration into the soil is slow and organic matter dissolution is possible. Root penetration is also extremely difficult.