pH will not tell you about N/P/K levels in the substrate, this can only be done through a laboratory specializing in soil analysis.
N = Nitrogen
P = Phosphorous
K = Potassium
These are the three "major" nutrients required for plant growth.
"Minor" nutrients are things like Calcium, Sulphur, Magnesium.
Trace elements, which are essential for plant health, but needed in only tiny amounts, include Copper, Iron, Manganese, Zinc, Boron, Chlorine and Molybdenum.
pH is a measurement of soil/substrate acidity or alkalinity. Less than 7.0 is acidic and over 7.0 is alkaline.
pH effects nutrient assimilation/availability to the plant.
Nutrient "lock out" in the true sense happens below 5.5 and above 7.5.
Judging the amount of N/P/K in your soil/substrate can only really be determined by the "visual health" of your plants and is only obvious when one of these nutrients is either too high or too low. Unfortunately, once it is too high or too low and by the time it shows up in your plants appearance, it is usually too late as the symptoms of high or low nutrients can take a few days/weeks to show up in the plants leaves. If your plant is growing "normally", then you soil/substrate is "in the zone" for plant health, but getting a precise N/P/K reading is not something that can be done at home by the average cultivator.
Hope this helps,.........
Organoman.