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The Groline HI-981421 monitor provides 24 hour continuous monitoring of pH, Conductivity (EC or TDS), and temperature in hyproponic nutrients.

Conductivity & TDS

£469.80 (exc.VAT)
£563.76 (tax incl.)
Full Description Specification

Quick to setup and simple to use, this monitor was designed with hydroponics, aquaponics, and greenhouses in mind.

Make your nutrient solution easy to manage with the Groline monitor and combined pH/EC/temperature probe.

Instantly view all measurements

The versatile display of the Groline monitor allows for three screen modes. The LCD can display all three essential hydroponic nutrients measurements at one time, a 3-second cycle of single measurements, or a real-time graph screen with options for measurement selection and log recall.

Monitor changes over time

Fluctuations in your hydroponic nutrient solution can have lasting effects on your plants. The Groline monitor automatically logs every 15 minutes for 30 days, and stores min, max and average values so you can recognise when patterns arise and help prevent future problems. For review and storage, use the USB-C to easily transfer data to a flash drive or PC using a cable. Files are exported as .csv.

Grow with confidence

The Groline monitor frees up your time by doing the testing for you. Simply set high and low alarm levels – if your hydroponic nutrient solution moves out of range a measurement error will display. A quick look at the large display will let you know if your nutrient solutions needs adjusting.


  • Can be integrated into a fertiliser system
  • pH/EC inline probe with built-in temperature sensor
  • IP65 rated enclosure designed to withstand harsh growing environment
  • Selectable EC to TDS conversion factor: Choice of either a 0.5 or 0.7 conversation factor
  • Automatic Temperature Compensation
  • Large LCD with plant-friendly green backlighting
  • Ambient light sensor for automatic LCD dimming
  • Quick calibration using Quick Cal solution simultaneously for pH and EC
  • Calibration reminder
  • Data logging for 30 days – logs every 15 minutes
  • Set up, calibration and operating parameters are stored in non-volatile memory. All settings are retained if power is lost
  • 24 hour summary screen (plot and details)
  • GLP feature calibration data for the pH and EC (up to 5 calibrations)
  • Alarms feature for all parameters

On-screen features

  • On-screen help at the push of a button
  • High and low alarms
  • Easy menu navigation
  • Data viewing
  • Data Transfer
  • Calibration timeout
  • GLP

About the Inline probe

The supplied HI-1285-9 multiparameter probe measures pH, EC and temperature in one convenient, rugged probe.

A solid-state preamplifier is integrated into the probe to protect the pH measurement from transient electrical noise. Sources of electrical noise include ballasts used in lighting and pumps to circulate water and nutrient solutions. The HI-1285-9 incorporates two graphite EC sensors for reliable conductivity readings.

Read More

pH Specifications
 pH Range0.00 to 12.00 pH
 pH Resolution0.01pH, (0.1pH)
 pH Accuracy±0.05pH, (±0.1pH)
 pH Calibrationone or two points calibration using standard buffers (pH4.01, 7.01, 10.01), using auto-buffer recognition, one-point calibration using quick calibration solution
 Temperature CompensationAutomatic
Conductivity – EC/TDS Specifications
 EC Range0.00 to 10.00 mS/cm
 EC Resolution0.01mS/cm
 EC Accuracy±0.1 mS/cm (0.00 to 5.00 mS); ±0.2 mS/cm – 5.00 to 10.00 mS/cm)
 EC CalibrationAutomatic recognition, one-point at 1.41 mS/cm or 5.00 mS/cm, one point calibration using quick calibration solution
 EC/TDS Temperature compensationAutomatic with β set at 1.9%/°C
 TDS Range0 to 5000 ppm (TDS conversion factor 0.5 (0.5 CF)); 0 to 7000 ppm (TDS conversion factor 0.7 (0.7 CF))
 TDS Resolution10ppm
 TDS Accuracy±2% f.s.
Temperature Specifications
 Temperature Range0.0 to 60.0°C
 Temperature Resolution0.1°C
 Temperature Accuracy±0.5°C
General specifications
 Display128 x 64 pixel B/W LCD with green backlight
 ConnectivityUSB Type-C – Export on flash drive/PC
 IP RatingIP65
 AlarmsHigh and low with enable/disable option for all parameters
 Data storageAutomatic logging for last 30 days at 15 minute intervals
 GLPLast 5 calibrations – pH and EC
 ProbeHI-1285-9 triple junction in-line pH/EC/TDS temperature PVC, pre-amplified multiparameter probe with internal temperature sensor, DIN connector and 3m cable
 Probe Max Pressure8 bar
 Probe range0 to 12pH
 Probe dimensions/weight187 x 25 x 25mm/191g
 Power supply12VDC adapter (included)
 Environment-5 to 50°; RH max 95% non-condensing
 Dimensions125 x 185 x 38mm
 Ordering InformationHI-981421 is supplied with HI-1285-9 multi-parameter probe, HI-50036-0 Quick Cal buffer solution sachet (2), HI-700661 pH electrode cleaning solution sachet for agriculture (2), DC Power adapter (1), and instructions.
 Warranty2 years (probe 6 months)
Compatible solutions:HI-50036p Quick Calibration Solution for GroLine pH and EC Meters, 25 sachets; HI-5036-023 Quick Calibration Solution for GroLine pH and EC Meters, 230 mL; HI-700661 GroLine Cleaning Solution for agriculture, 230 mL; HI-70300-023 GroLine Electrode Storage Solution, 230 mL. HI-7004-023 GroLine pH 4.01 Calibration Buffer, 230 mL; HI-7007-023 GroLine pH 7.01 Calibration Buffer, 230 mL; HI-7010-023 GroLine pH 10.01 Calibration Buffer, 230 mL.

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