The question on this page is not which brand, but whether you want one instrument or two. Everything here reads pH, EC and temperature from the same sample. That saves a step and removes a source of error. There is something on the other side of that too, and it is the more honest half of the story.
One sample, one moment
With two separate meters you are measuring twice: you scoop, read the pH, put that meter down, pick up the next. In between, the tank may have been stirred or topped up. A combo meter gives you three values that belong together because they came from the same water at the same moment, which is what makes them comparable week to week.
What you give up for it
It all sits in one housing, so if something fails you lose both readings, and you cannot replace one half with something better. A combo meter does not take calibration off your hands either: the pH side is still an electrode that drifts and that you calibrate on two points, exactly as with a single pen. If you would rather have two separate instruments, they are under pH Meters and EC Meters.
In the hand
The Bluelab Combo reads pH, EC and temperature. The Combo meter Plus is the same meter with the Leap probe, and that is the whole difference: the hardened tip also reads in soil, coco and rockwool, so you are measuring your root zone and not only your feed water. Milwaukee's MW806 Max does pH, EC, TDS and temperature on one electrode and logs over USB to a computer, which is what you need when you want to trace a slowly drifting value rather than guess at it.
Permanently at the tank
Milwaukee's MC811 Max is not a handheld: it sits at the nutrient tank, the electrodes stay in, and three displays show pH, EC and temperature continuously. The Bluelab Guardian Wifi does the same and lets you watch remotely, which pays off mostly in the hours you are not there. If you carry a handheld around the room, the Carry Case fits your Bluelab meter closely enough that you can read it without taking it out.
Frequently asked questions
Is a combo meter less accurate than separate meters?
Not by definition. Accuracy comes from the electrode, not from how many values the screen shows. Compare the stated accuracy per model, exactly as you would with a single meter.
Can I measure in my pot with one?
Only with the Combo meter Plus, thanks to the Leap probe. The other combo meters are built for liquid, and substrate damages an ordinary glass bulb.
What if the pH side gives out?
On Bluelab the electrodes are available separately, so you replace the probe rather than the meter. Calibration and storage fluid keep that moment furthest away, and both are under Calibration Fluids.
