Measuring & Control — pH Meters

Almost every meter here reads pH to a tenth or a hundredth. The difference is not in the screen but in the electrode: what you may push it into, how accurate it is, and whether you can replace it on its own. Choose on that, and what you replace later is a tip rather than a meter.

Pen, monitor or kit

A pen measures when you pick it up: the Bluelab pH pen, and from Milwaukee the MW100, PH51, PH55 and PH600. A monitor measures when you are not there: Milwaukee's MC110 and the Bluelab Guardian Wifi, read remotely. To start complete there are kits, from AC Infinity the Digital pH Meter Kit and the pH Meter PRO Kit, the Bluelab Starterpack, or the Milwaukee case holding the MW710, MW100 and MW302. Meters reading pH and EC together, the Bluelab Combo, Milwaukee's MC811 Max and MW806 Max and the AC Infinity Hydroponic Meter PRO Kit, are under Combo Meters.

Accuracy is a choice

The PH51 states ±0.1 pH, the MW101 ±0.02 with two-point calibration. For nudging a reservoir back into line, a tenth is plenty; work to a chart with a narrow window and that factor of five is the difference between knowing and suspecting. Look at the stated accuracy rather than at how many decimals the display shows.

In water or in your medium

A standard electrode is built for liquid. For soil, coco or rockwool you need a tip that tolerates it: the Bluelab soil pH pen, the Multimedia pH meter that reads in the solution and in the root zone, or Milwaukee's MW101 with its SE220 soil probe. For moisture and nutrient status in the medium, see Soil Meters.

The electrode is the wear part

Whether the tip can be replaced separately is a question you ask when buying, not when it happens. At Bluelab the pH electrode with BNC connector is sold on its own for the pH meter, the Combo and the Guardian, and the Leap fits every Bluelab meter, with a tip rated for substrate too. On Milwaukee you replace the PH55's yourself. How long a tip lasts is then down to calibration and storage fluid from Calibration Fluids.

Frequently asked questions

Should I calibrate a new meter straight away?
Yes. A meter does not arrive set to your conditions, and the first reading is precisely the one your schedule gets based on.

My pen has gone slow. Is it finished?
Not necessarily. A slow or restless electrode is usually dirty or dried out, and cleaning and recalibrating comes before replacing. If it still will not hold calibration after that, it is at the end.

Do I need a monitor, or is a pen enough?
That depends on your system. If you mix fresh for every watering and discard the rest, a pen measures at exactly the right moment. If your solution stands or recirculates, the pH shifts during the hours nobody is looking.