Bluelab Conductivity Pen Review: EC, PPM & Temperature

Quick answer: The Bluelab Conductivity Pen is a solid spot-check meter when you want a numeric EC or PPM reading plus solution temperature. I liked its finer display more than the Truncheon’s LED scale, but my 2022 “always add 50 PPM” workaround was not a valid calibration method. The right workflow is to choose one scale, keep the probe clean and verify it with a known conductivity standard.

Watch the original HWGrow PENCON review

Current Bluelab Conductivity Pen specifications

These are the manufacturer’s current specifications, not measurements from my short video. Check the current Bluelab product page and manual before buying because models and warranty terms can change.

The important correction: do not automatically add 50 PPM

In the video, my unit did not display the very small changes I expected at the low end, so I said to add 50 PPM to every reading. That was an observation about one meter in one comparison—not a valid correction factor.

A fixed adjustment can hide a dirty probe, a scale mismatch, temperature differences or an unverified comparison meter. Rinse the probe, let the reading stabilize and test it in the correct conductivity standard. If it falls outside the manufacturer’s acceptable range after cleaning, follow the current calibration or support procedure. Do not invent an offset.

EC, PPM 500 and PPM 700 explained

The meter is sensing conductivity once. PPM 500 and PPM 700 are different mathematical conversions of that EC reading, which is why two meters can show different PPM numbers in the same solution without either one necessarily being broken.

When possible, record EC. If you prefer PPM, write ppm 500 or ppm 700, not just “PPM.” Bluelab’s conductivity-scale explanation confirms that both PPM displays are conversions of overall ionic conductivity.

What I liked

• Readable numeric display. It is easier to log than an LED range.
• Multiple scales. You can match EC, ppm 500 or ppm 700 records without doing mental conversions.
• Temperature on the same tool. That helps you wait for the probe and solution to reach a stable reading.
• Waterproof, floating body. Useful around reservoirs, although it should not be left in the solution.
• Compact spot checks. Better suited to jars, buckets and samples than a long mixing wand.

What I would change

I still want clearer performance at very low conductivity, especially when I am comparing small ingredient additions. But a display with more digits is not automatically more accurate. Resolution tells you the smallest displayed step; accuracy tells you how close the result is expected to be under specified conditions.

The pen also measures conductivity and temperature, not pH. A cheap three-in-one meter can be convenient, but price and extra modes do not prove better accuracy. Verify any meter against known standards before trusting it with a crop.

How to use and care for it

1. Choose EC, ppm 500 or ppm 700 and keep the same scale in your records.
2. Rinse the probe with clean water before and after the sample.
3. Place the probe in the fully mixed solution and wait for the temperature and reading to stabilize.
4. Do not touch the sensing face with your fingers.
5. Clean the conductivity probe when residue or a failed standard check indicates it needs attention.
6. Verify it with fresh conductivity standard and follow the current manual for optional calibration.
7. Measure pH separately after the complete nutrient solution has stabilized.

Use the HWGrow pH, EC and PPM guide to interpret the numbers and the meter-care guide for cleaning, standards and storage. The meter supports a decision; it does not diagnose a plant by itself.

Recommended conductivity tools

Bluelab Conductivity PenNumeric EC, ppm 500, ppm 700 and temperature spot checks. Verify the current PENCON model and warranty.
Buy It Now



2.77 EC conductivity standardUse a fresh compatible standard to verify the clean probe instead of guessing a fixed PPM correction.
Buy It Now



pH and EC meter kitA lower-cost alternative for measuring both acidity and conductivity. Calibration and care still determine whether its numbers are useful.
Buy It Now

Affiliate disclosure: HWGrow may earn a commission from qualifying purchases at no additional cost to you. Product destinations can be replaced with equivalent current items; verify the exact model and compatible standard.

Bluelab Conductivity Pen FAQ

Does the Bluelab Conductivity Pen measure pH?

No. It measures conductivity and solution temperature. Use a separate pH meter or a verified combination meter for pH.

Should I add 50 PPM to every reading?

No. That was an unsupported workaround in the historical video. Clean and verify the probe with a conductivity standard, confirm the selected scale and follow the current calibration instructions.

Which PPM scale should I use?

Use the scale that matches your chart and records. EC is easier to compare across devices because ppm 500 and ppm 700 are different conversions of the same conductivity reading.

Does a more detailed display guarantee better accuracy?

No. Display resolution and measurement accuracy are different. Check the published accuracy and verify the meter against a known standard.