While it is generally recommended to maintain the pH between 5.5 and 6.5 (+/- 0.5) for the sake of the plant, pH has very little impact on nutrition in plants that are not grown in soil.
pH affects the cation exchange capacity (CEC) of soils, that is, their ability to trap nutrient ions and how strongly they are held, which of course, affects their availability to the plants. Orchid media have almost no CEC, and certainly "air" doesn't.
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