Well, you can get a
meter, they are portable, and they run on batteries, and need to be stored correctly, and need to be calibrated often because they are stored outside of the nute solution.
Or you can get a
monitor. They run on AC power, so not as portable, but the electrode stays in the res, so you can always see what the pH is. Because the electrode is in the res, it stays in calibration better.
HTH