About a year ago, I got a Hanna PHEP-5, which is a pen-type meter that takes replaceable electrodes. After a couple months, the first electrode began giving varying measurements, so I got a replacement electrode. After a couple of months, it was getting slow to respond, and then the Hanna meter broke. So I bought a used Beckman meter on eBay that takes standard BNC-type electrodes, and bought a refillable $150 electrode back in August. It's doing fine.

I found that all electrodes can take 15-20 minutes for a measurement to stabilise. To save time, I put the electrode in old developer (or XTOL) while mixing new developer, so that the electrode is already acclimated when I need to take a measurement, so the measurement only takes 1-2 minutes.

My electrodes are always stored in KCl solution. After use, I rinse well with tap water, dry the case (without touching the bulb), and put back in KCl solution. I need to get some cleaning solution for electrodes.

I'm trying to measure with an accuracy of +-.02, so I'm being careful with calibration and temperature. If the cal isn't too old, I'll do a quick cal as part of the acclimation using XTOL. I know XTOL is 8.20 or 8.21, so I measure the mV (millivolts) of my test-developer and calculate the pH-difference from XTOL. In essence, this is a one-point cal and it works well because the pH-difference with XTOL is small so a small slope-drift won't matter. This sounds complicated, but in practice it's easy and I get double-use out of the acclimation-period.

BTW, I fixed the Hanna meter simply by taking it apart and letting it air-out. The seal at the electrode leaked a little, letting moisture get into the electronics. I am not impressed with its design.

I suggest buying a new or used meter that accepts electrodes with standard BNC connectors. Then you can get any kind of electrode(s) you want without replacing the meter.

Mark Overton