Well, pH isn't measured in ppm. It is the abbreviation for power of Hydrogen. A pH of 7.0 is neutral. Below that is acidic. Above that is alkaline (or basic). Parts per million, ppm, measures the amount of a substance in a solution or mixture.
People do say soil can buffer the pH. That means the soil will adjust the pH to a specific value.
There isn't a need for adjusting the pH of water when using organic (dry) nutrients. There is a need, however, when using synthetic (liquid) nutrients. The reason for the difference has to do with how the nutrients are taken up by the roots.
Synthetic nutrients are directly taken up by the plant, but the best pH value differs for each elemental nutrient (Nitogen, for example). Only a pH close to 6.0 is at a level at which all nutrients are available to the plant.
Organic nutrients are taken up with the help of fungi in the soil, known as mycorrhiza. Mycorrhizae live in mutualistic symbiotic relationship with the plant. Their part in this relationship is to feed the plant, thus pH is only a concern for the mycorrhizae, and they aren't as picky as the plant.