BlueLab Combi PH, EC and Temperature meter

Portable meter with two separate probes: one for acidity, one for conductivity and temperature. Runs without mains power, five-year warranty on the meter.

The Bluelab Combo Meter gives you the three values a crop is steered on in one instrument. You pick the reading with a button, hang the probes in the solution and read off. The pH probe is replaceable, which means the meter lasts you years while the wear part can come out.

The conductivity probe needs no calibration. It is locked at manufacture and measures between two fixed electrodes, where nothing ages. The pH probe calibrates at three points with a button press; the instructions are printed on the back of the meter itself.

Temperature: the third reading everyone ignores

Almost nobody buys this meter for the temperature. Yet it is the value that most often explains why the other two are not doing what you expect.

Three things happen at once as your solution warms up.

Less oxygen fits in the water. That is physics, and it bites harder than you would expect. Roots suspended permanently in solution take all their oxygen from it, and above 22 °C the margin gets thin. Above 24 °C you also start dealing with root rot pathogens that thrive in warm, oxygen-poor water. Those two effects reinforce each other.

Your EC reading shifts with it. Conductivity rises with temperature. The same solution reads higher warm than cold. This meter compensates automatically, so you see the corrected value, but that only works because temperature is being measured alongside.

Uptake changes. Too cold and the plant takes up slowly; growth is close to stalled below 16 °C. Between 18 and 22 °C you are in good shape.

Worth knowing on this meter: the automatic temperature compensation applies to the EC reading, not to pH. The quoted ± 0.1 pH accuracy is specified at 25 °C. If you measure a considerably colder or warmer solution, expect the pH reading to carry some of that. In a grow room sitting between 18 and 22 °C it is negligible; with outdoor water in spring it is not.

Technical Specifications:

• Measures: pH, EC, temperature, CF, ppm 500 (TDS) and ppm 700
• pH range: 0.0 to 14.0 pH
• resolution: 0.1 pH
• accuracy: ± 0.1 pH at 25 °C
• pH calibration points: 3: pH 4, 7 and 10
• EC range: 0.0 to 9.9 EC
• resolution: 0.1 EC
• accuracy: ± 0.1 EC
• EC calibration: not required and not possible; checkable against EC 2.77
• Temperature range: 0 to 50 °C: automatic compensation on EC
• Probes: separate pH probe (replaceable) and conductivity/temperature probe
• Power: 2 x AAA battery (included), no mains needed
• Supplied with: pH 4 and pH 7 buffer sachets
• Warranty: 5 years on the meter, ½ year on the electrodes

Frequently asked questions

Why only six months warranty on the probes?
Because a pH probe is a consumable, not an appliance. How long it lasts depends mostly on storage and cleaning: keeping it wet with KCl storage solution makes the biggest practical difference.

Can I measure soil or coco with it?
Not with the standard probe. To read the medium, look at the Combo Meter Plus, which ships with a Leap probe.

Does it work without a socket?
Yes, it runs on two AAA batteries. That makes it usable anywhere, including places with no power.

What is the difference from two separate pens?
Probes on cables, so you can measure in a deep reservoir without holding the meter in the water, and a replaceable pH probe. Two pens are more compact and cheaper.

How often should I calibrate?
The pH probe monthly. The conductivity probe not at all. At most you check it against EC 2.77.