Water can be either neutral, acidic or basic.
The pH scale is the measurement of how acidic or basic water is, ranging from 0 to 14. 7 is neutral—neither acidic nor basic. A number lower than 7 is acidic. A number higher than 7 is basic.
Acidic means there are more hydrogen ions than hydroxide ions in a solution. Basic means there are more hydroxide ions than hydrogen ions in a solution.
Acidic substances add hydrogen ions to a solution making it more acidic. Alkali substances take ions away from a solution making it more basic.
Substances added to water that are acidic or alkali modify the pH of water.
The pH value of a solution affects a plant’s ability to absorb minerals. For example, plants struggle to uptake manganese, phosphate, and iron when a feeding solution is too basic.
pH also has an effect on the solubility of minerals. Minerals are soluble when water has a pH of 5.6-6.4. If pH drifts out of this range, minerals can precipitate out of solution. For example, calcium, iron and phosphate start to leave solution when pH rises above 6.5.
The pH of a feeding solution for cannabis plants should be kept between 5.8-6.3. This range optimizes mineral solubility and uptake.
The pH of water is measured using an electronic pH meter. pH meters must be calibrated before use using calibration solutions.
Growers adjust the pH of their solutions with commercially available pH Up and pH Down solutions. pH Up is a concentrated base that raises pH. pH Down is a concentrated acid that lowers pH.
pH up and down solutions are very concentrated and are best administered to water with a syringe or dropper.