I guess I'm old school. I don't have any ph monitors on my reactor or tank. I keep an eye on the bubble counter, the effluent drip rate, and do occasional tests on effluent for dkh. I do test tank h2o for Ca, dKH, and PH, but I've learned that if my alk/Ca is correct for the tank, then the ph is fine and stable also. If Ca or Alk are a little off on my tank, then I test the effluent and make corrections as needed.