Prepare your Water Quality Sonde for Monitoring Season!

The prime water quality monitoring season is upon us, and that means making sure that your water quality sonde is ready to provide the accurate measurements you know and expect from OTT Hydromet equipment.

If the equipment has been stored over the winter, it is important to prepare the sensors before the first use of the season. Below are a few tips to remember when preparing your equipment for service:

  • When dealing with equipment using  batteries, assure fresh batteries of the same brand are used and positioned correctly in the unit. Remove batteries when the unit is not in use the winter period.
  • It is important to verify proper operation of the temperature probe as some sensors are temperature compensated. Test the sensor in a water bath of a known temperature. If the temperature is out of spec, it cannot be calibrated and must be sent in for service.
  • If using a pH sensor: it is recommended to replace the electrolyte and KCl salt pellets inside of the reference. Make sure the Teflon junction is clean and passes reference electrolyte solution readily. If the reference junction appears discolored, clogged, contaminated, or if slow probe response time persists after cleaning the pH sensing bulb, then often the best practice is to replace the reference junction.
  • If using a self-cleaning turbidity sensor: verify the operation of the self-cleaning motor before calibration is performed, as the wiper helps remove any bubbles or buildup that can affect sensor readings
  • The conductivity sensor must be calibrated before LDO and depth sensors
  • If using the LDO sensor: the cap should be inspected for wear and scratches. We recommend that the LDO cap be replaced yearly; however this could be more or less frequent depending on use.
  • If using the Clark cell DO sensor: the electrolyte and membrane should be replaced. Take note that the membrane must soak in clean water for a minimum of 4 hours to allow the membrane to relax before calibration. The Clark cell requires a 2-minute warmup time before measurements should be taken.
  • It is recommended to give the Ion Selective Electrodes (ISE) a 2-minute warmup time, and they should be calibrated after pH, ORP (if equipped), and conductivity. A longer warmup time of approximately 5 minutes may be necessary to allow the readings to be stable. ISE tips last ~6 months of moderate use. For NH4 and NO3 sensors, it is recommended that the tips are hydrated for 24 hours in the high concentration of the associated standard. Chloride sensors should be stored in a dark environment when not installed on the sonde.

hydrolab datasonde 5x
Equipment should be cleaned every time before sampling for the most accurate readings. It is a good idea to check linearity on most sensors with a mid-range standard if at all possible. By doing so, you are improving the accuracy of your calibration standards, the soundness of your calibration practices, and the proper function of your sonde’s sensors.

When calibrating and sampling, please remember to allow the sensor’s readings to stabilize, AND to allow the temperature readings to stabilize as well. Only fresh standards of known values should be used, and standards should never be reused for calibration.

For calibration guidance, please refer to the sensor calibration and maintenance videos on our Youtube page.

After sampling, it is important to clean and rinse the equipment in addition to performing a post check with standards to verify that the readings are still accurate, as this adds a level of quality assurance to the data collected. After any sampling and post checks, all water quality sensors should be stored in clear pH 4 buffer to prevent the sensors from drying out and becoming damaged. To save standard, it is acceptable to use the discarded pH 4 used in calibrations for storage.

If you need additional information on preparing, calibrating, and maintaining your equipment, please refer to the instrument’s user manual, and feel free to call OTT Hydromet Technical Support at 800-949-3766 option 2, or email them at

Should you need to order any additional calibration standards, equipment, or materials, please contact our sales department at 800-949-3766 and choose option 2, or email

Should you desire factory performed PT&E, we currently offer a Service Plus plan to US customers which allows you to send your equipment to our Loveland, CO facility for convenient maintenance, calibration, and PT&E of your Hydrolab equipment by our trained service technicians.

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