by Jorge Cervantes
pH
The pH scale, from 0-14, measures acid-to-alkaline balance. Zero is the most acidic, 7 is neutral, and 14 is most alkaline. Every full-point change in pH signifies a tenfold increase or decrease in acidity r alkalinity. For example, soil or water with a pH of 5 is 10 times more acidic than water or soil with a pH of 6.
Different mediums perform best at different pH levels. Follow manufacturer’s guidelines for pH level, and correct the pH using the manufacturer’s suggested chemicals.
Stabilize the pH of the water before adding fertilizer. Make a correction if readings vary plus/minus one-half point. Deviations in pH levels often affect nutrient solubility.
Use an electronic pH meter to measure water and nutrient solution pH. You can also measure the pH of soil, soilless substrates, and water and nutrient solutions with an electronic pH pen when the substrate is mixed with water.
Fine dolomite lime, a compound of magnesium (Mg) and calcium (Ca), keeps the soil pH stable. Add 1 cup per cubic foot to keep potting soil pH stable.
Hydrated lime is only calcium and water-soluble. Be very careful when using and do not use more than 0.25 cup per cubic foot.
Raise water and nutrient solution pH with calcium carbonate, potassium hydroxide, or sodium hydroxide. Both hydroxides are caustic and require special handling.
Lower water and nutrient solution pH: Phosphoric and nitric acid can be used to lower pH, as can calcium nitrate, but it is less common. Aspirin also lowers the pH. However, hormonal reactions appear to be triggered by aspirin. Some growers report more hermaphrodites when using aspirin to alter the pH.