If you haven’t already, make sure to read Part 1
Understanding pH Readings
Acids have a low pH, and bases have a high pH, pure water sits in the middle at 7. The lowest number on the pH scale is 0, which is a very strong acid, and the highest is 14, which is a very strong base.
The pH scale is logarithmic, not linear. Each full number difference is a factor of ten in difference. For example, pure water has a pH of 7, a pH of 6 is a 10 times stronger acid, and a pH of 5 is 100 times stronger.
To check the pH of your nutrient solution, either use a meter, or a General Hydroponics pH Test Kit. To use the test kit, fill the test vial halfway with the solution to be tested, and add 3-5 drops of the pH test indicator fluid. Cap the vial, and tap the side while holding lightly to mix. Compare the color of the liquid to the colors on the label. If the resulting fluid is yellow, the pH is around 6.0 and acceptable to use. Orange or red indicate low pH, add pH UP in increments of 1-2 ml per gallon, giving each treatment time to disperse before retesting. Green or blue indicates high pH, add pH Down as above to lower pH.
Since the test fluid is only used at a few drops at a time, the bottle that comes with the test kit lasts for many tests, and does not require batteries or calibration.