opinions on American Marine Pinpoint pH meter

[astroboy]

Any ideas on how reliable? I calibrated mine the best I could (calibration solutions 7.01 and 10.01) and it says my tank has a pH of 7.65, which is possible, I suppose, except that the vivosun pencil pH meter I have says it's 8.1, so a difference of 0.45. The vivosun gave readings on the calibration solutions of 7.2 and 10.2. I did the measurements/calibrations with two different sets of solutions. So, something is wrong. The solutions, which came in sealed packets, were three years old. Do those go bad after a while?

 

Anyway, does anyone have an opinion on the American Marine meter? I used to have another one years ago and I never got measurements that I trusted. If the $15 pen meters work just as well I'm greatly tempted to toss it.

[zygote2k]

How old are the probes?

calibrating with old probes can yield wildly varying results.

American Marine ph meters have been around 35+ years. 

[astroboy]

The probe is only a few weeks old. The meter itself where the probe connects to is very slightly corroded. I'll see if I can clean that up and it if makes a difference. I recalibrated with some brand new solution, it seems to be working OK for now....