The Bluelab Conductivity Pen is a handheld meter that tells you how strong your nutrient solution is. It reads conductivity over 0.0 to 10.0 EC and the maker lists it as measuring conductivity in EC, ppm 500 (TDS), or ppm 700, with temperature readable in °C or °F. Readings are corrected for solution temperature by Automatic Temperature Compensation (ATC), using the pen’s integrated temperature sensor. It is a solution spot-check instrument — not a nutrient, a pH meter, or a substrate probe.
What it is
Bluelab’s entry handheld for nutrient strength carries the maker model code PENCON. The maker describes it as an accurate and reliable conductivity (EC) and temperature pen for measuring nutrient levels and temperature to manage the nutrient strength in the root zone, and positions it to pair with the Bluelab pH Pen for a complete measurement system. This pen does not read pH.
Full technical specifications
| Maker model code | PENCON |
|---|---|
| EC range | 0.0–10.0 |
| EC resolution | 0.1 |
| EC accuracy | ± 0.1 |
| ppm 500 (TDS) range | 0 – 5000 |
| ppm 500 (TDS) resolution | 10 |
| ppm 500 (TDS) accuracy | ± 50 |
| ppm 700 range | 0 – 7000 |
| ppm 700 resolution | 10 |
| ppm 700 accuracy | ± 70 |
| Temperature range (°C / °F) | 0–50 / 32–122 |
| Temperature resolution (°C / °F) | 1 / 1 |
| Temperature accuracy | ±1 / ±2 |
| Operating environment (solution) | 0 – 50 °C / 32 – 122 °F — the maker states not to use or store the pen outside this temperature range |
| Temperature compensation | Automatic Temperature Compensation (ATC) via the integrated temperature sensor |
| Selectable units | EC, ppm 500 (TDS), or ppm 700 for conductivity; °C or °F for temperature |
| Calibration | Factory calibrated and ready to use immediately |
| Power | 1x AAA alkaline battery |
| Box contents | 1x Bluelab Conductivity Pen |
Accuracy figures are the maker’s at a reference temperature of 25°C / 77°F.
Why choose this pen
- Survives the reservoir. The maker lists it as waterproof, and states it floats in any solution.
- Readable in a dim room. It has a bright, easy-to-read backlit display.
- Nothing to set up. It is factory calibrated and ready to use immediately.
- Compact by design. The maker lists a compact handheld design for convenient use.
What it fits and works with
- Nutrient solution, not substrate. The maker’s comparison lists its growing method as Solution, its type as Handheld, and its parameters as Conductivity (EC) and Temperature.
- Pairs with a pH instrument. The maker directs you to combine it with the Bluelab pH Pen to also measure pH.
- Match your nutrient label’s scale. Before measuring in ppm the guide says to know what ppm scale your meter is using, which calibration standard to use for it, and what ppm scale your nutrient is referring to.
- Consumables. The guide names the Bluelab Probe Care Kit – Conductivity, containing probe care instructions, two 20 ml Bluelab 2.77 EC Standard Solution single-use sachets, the Bluelab Conductivity Probe Cleaner and Chamois, and a plastic cup.
How to use it (maker directions)
Every step below is printed in Bluelab’s care and use guide for this pen.
- Power on and off. Press the power button to turn the pen on; the last measurement is recalled for 3 seconds. Press and hold the power button until OFF is displayed to turn it off, and note that the pen automatically turns off after 4 minutes to conserve battery power.
- Take a reading. Place the probe in the solution and wait for the reading to stabilize.
- Freeze a reading. Short press the power button to hold the reading on screen; press it again to exit the hold function.
- Switch units. Hold the units button for 3 seconds until the conductivity and temperature units flash, then short press it again to cycle between unit combinations; the screen exits the mode when no button is pressed for 3 seconds.
- Rinse after every use. Rinse the conductivity probe under running water after each use to reduce the build-up of nutrient salts, and clean the probe once every two weeks to ensure accurate readings.
- Clean the probe face. The guide directs you to remove the shroud, place one or two drops of probe cleaner on the probe face and rub firmly with a finger or Bluelab Chamois, rinse off all traces of cleaner under running water, check that water forms a film on the probe face with no beads (repeat if beading is present), then replace the shroud and test in a known solution. It also warns to use the Bluelab Conductivity Probe Cleaner or an unscented liquid scourer cream, never a scented variety, because scented products contain oils that contaminate the probe.
- Battery. Battery life is expected to be 350 hours, rechargeable batteries are not to be used, and the battery cap fasteners must be tightened until no space is left between cap and body so the unit stays waterproof.
- Calibration is optional. The guide states that calibration of conductivity is not required for this unit because it is factory calibrated, but if you wish to calibrate you must clean the probe first, rinse it in fresh water, place it in a known standard solution, wait for the reading to stabilize, then hold the cal button for 3 seconds until CAL appears. For the standard solution itself the guide gives a solution value of 2.77 EC / 1385 ppm 500 / 1940 ppm 700, displaying as 2.8 EC / 1390 ppm 500 / 1940 ppm 700.
Virginia Cooperative Extension explains that EC measurement lets the grower know if the total amount of fertilizer in solution has changed over time, and reports that many leafy greens perform well at EC 1.2 to 2.0 mS/cm.
Bluelab’s summary is that the instrument is only as accurate as the probe is clean, and the conductivity probe must be cleaned regularly to remove built-up nutrient salts.
How it compares in Bluelab’s handheld range
Only what Bluelab’s own side-by-side states — role, not ranking.
| Factor | Conductivity Pen (this product) | Commercial Truncheon Nutrient Meter | Combo Meter |
|---|---|---|---|
| Parameters measured | Conductivity (EC) and Temperature | Conductivity (EC) only, handheld, recommended for commercial growers | Conductivity (EC), pH and Temperature, handheld |
| Recommended for | Home growers | Commercial growers, per the same maker comparison | Home growers, per the same maker comparison |
| Connected / app | Not connected | Not connected | Connected |
Questions the maker’s guide answers
Does it support every ppm scale? No. The guide for this pen states that this unit does not measure in the 540 ppm scale, and that to test or calibrate in a 1500 ppm solution you must set the pen to EC and then multiply your result by 540 (calibrating, 2.8 x 540 = 1512).
How accurate are the ppm readings? The guide states that the true ppm of a solution can only be determined by chemical analysis, ppm cannot be accurately measured by an EC meter, and the ppm scales are present on Bluelab products as a conversion guide only. It explains the scales it does carry as the ppm 500 scale being based on measuring potassium chloride (KCl) content and the ppm 700 scale on sodium chloride (NaCl) content, with the maker’s own worked conversions 2.4 EC x 500 = 1200 ppm (500 scale) and 2.4 EC x 700 = 1680 ppm (700 scale).
My readings look low. Is the pen broken? Usually not. The troubleshooting guide says low readings usually mean the probe is contaminated, so clean the probe and retest in a known solution using an unscented cleaner, while high readings call for calibrating the pen in a known standard solution.
Dialling in a reservoir? Add to cart or talk to a grower.
Sources
- Bluelab — Bluelab Conductivity Pen maker product page (HTTP 200 via WAF-immune fetch_maker, retrieved 2026-07-19; PRIMARY source). Supports the model code, every specifications-table value, the feature list, ATC, and the handheld comparison: https://bluelab.com/products/bluelab-conductivity-pen
- Bluelab — Bluelab Conductivity Pen “Care and use guide” (document PENCON_EN_V3_020522), the product manual linked from the maker product page, on Bluelab’s asset host (HTTP 200 via fetch_maker, retrieved 2026-07-19). Supports every operating, cleaning, battery and calibration instruction here, plus the scale and troubleshooting answers: https://files.plytix.com/api/v1.1/file/public_files/pim/assets/89/90/94/62/629490895d155f1bc7e496a7/texts/40/00/02/63/63020040e65d7411b3de2c50/BL_ENG_Manual_Conductivity-Pen.pdf
- Virginia Cooperative Extension (Virginia Tech) — “Deep Water Culture (DWC) Systems”, SPES-464 (HTTP 200, retrieved 2026-07-19; Tier-1 authority for EC-monitoring context only, no product spec): https://www.pubs.ext.vt.edu/SPES/spes-464/spes-464.html
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