Because the pH of the solution is a value that indicates the ability of the roots to
absorb various nutrients. In the nutrient solution. I normally try to maintain the pH at 5.8 to 7.0, because the values or ranges of plant nutrients. It's a solution that can be applied to plants, the pH of the nutrient solution was changed due to several reasons such as changes in plant roots absorb nutrients in the nutrient solution. Which plant release hydrogen (H +) and Hydroxide (OH-) from the root to the nutrient solution the pH change.