Potential Hydrogen, commonly known as pH, is a number that indicates the acidity (below 7.0pH) or alkalinity (above 7.0pH) of a solution.
It is important to maintain a hydroponic nutrient solution at a pH where elements in the nutrient solution are most available to the plant.
Each element has a pH range in which its availability is maximised.
In hydroponics, the range in which most elements are available is typically between 5.5pH and 6.5pH.
Strong acid (low pH) or strong alkali (high pH) conditions can upset the balance of a nutrient solution.
This can cause a loss of uptake for specific nutrients by the plants roots.
This is know as "lockout", whereby certain elements become unavailable to the plant due to pH.