TT-920: In-line pH Probe Care and Meter Calibration

Tech Tip-920

Models Affected: RNS-4-SS

Proper care of RNS-4-SS pH monitoring components.


Consistent monitoring of pH levels and proper care of pH monitoring components are very important steps when assuring smooth operation, preventing part failures, and extending the overall life of your Recirculation/Neutralization System (RNS) system. Improper pH levels in the RNS holding tank account for approximately nine out of ten component failures. The pH level should never drop below 5.0 or rise above 9.0. Allowing the pH level to fall outside of these parameters may result in premature failure of the sump pump and float switch located in the Battery Wash Cabinet. Left unchecked, further damage to the relief valve and system pump are likely. Also, highly acidic water may drip from recently washed batteries creating a hazardous environment for personnel and cause damage to your battery extractor, stands, and battery room floor. In order to ensure the correct pH readings are displayed during tank water testing, it is essential to properly maintain and calibrate the pH probe and meter.

The most critical aspect in maintaining accurate and consistent pH monitoring is to keep the pH probe wet, either in the solution which it was shipped, a buffer solution, or in its mounted position on the RNS. If allowed to dry out, irreparable damage to the probe will occur. In its mounted position, it is possible for an air pocket to form around the pH probe when water flow is interrupted for times of service such as filter cleaning/replacement or water change.


The pH meter should be calibrated weekly. Air must be purged from the pH probe mounting socket if the water is drained and replaced, or when any maintenance is performed to the plumbing system causing water loss. If the RNS is to be left without water for more than a few hours, the pH probe should be removed from its socket and stored in a soaker bottle or rubber boot containing pH buffer 4.0 or 7.0 solution. DO NOT use distilled or deionized water as this will drastically reduce the probe’s lifespan.


  • If the probe has dried out, it may be possible to rehydrate the probe by soaking it in buffer 4.0 solution for up to 2 hours. If the probe will not rehydrate, contact BHS Tech Support Department for a replacement probe.
  • Refer to the pH meter manufacturer’s instructions included with the unit for calibration procedures.
  • Refer to “pH PROBE INSTALLATION” in the RNS-4-SS Parts and Service Manual for instructions to properly purge any air from the pH probe mounting socket.

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