PH is a measure of the acidity or alkaline quality of the water or soil. The pH scale runs from one, which is highly acidic, to 14, which is highly alkaline. Seven is neutral. Every tenth of a point is a significant increase in the pH level.
If you are using a hydroponic system, the water's pH should be kept between 6.1-6.3, which is mildly acidic. Soil has a little more latitude, but should be kept within 5.9-6.4. When rockwool is used, keep the pH at the lower end of the recommended measure to counteract rockwool's strong alkalinity.
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