I have been using a pH meter of the kind commonly available in garden centres - it was a replacement for one that I wasn't sure was reliable.

It turns out that it's completely useless. I discovered today when I plunged the probe into a lemon, only to find that it read pH 8! I then tested it in 5% (0.5M) acetic acid (white vinegar) and it read pH 10. This is complete nonsense, of course!

This may be a 'two off' experience, but the meter is obviously completely oddball. It does correctly read neutral values, but I wonder if both circuits are reading positive because of an electronic defect.

Clearly, any corrective interventions I may have made if I'd relied on the meter would have been disastrous for my plants!

On 8 June, 22:12, Homer Sparrow Homer.Sparrow.
wrote:
I have been using a pH meter of the kind commonly available in garden
centres - it was a replacement for one that I wasn't sure was
reliable.

It turns out that it's completely useless. *I discovered today when I
plunged the probe into a lemon, only to find that it read pH 8! I then
tested it in 5% (0.5M) *acetic acid (white vinegar) and it read pH 10.
This is complete nonsense, of course! *

This may be a 'two off' experience, but the meter is obviously
completely oddball. *It does correctly read neutral values, but I
wonder if both circuits are reading positive because of an electronic
defect. *

Clearly, any corrective interventions I may have made if I'd relied on
the meter would have been disastrous for my plants!

--
Homer Sparrow

If you were a regular reader here you would have seen me posting about
this problem a few times.
If you are handy with a saldering iron then all you need to do is to
open it up and swap the two wires around then it will read OK.
David hill

Hi David,

As it happens, I'm very handy with a soldering iron However the unit is factory sealed in a way that makes it difficult to open without damaging it. Please can you post me a link to one or more of your previous posts on the subject? I'm also interested in electronics, btw.

Thanks,

Actually, it proved fairly easy to lever open the case. I've now reversed the polarity of the meter and all is fine.

I can't believe these things were sold without having a basic check in the factory!

Thanks, Chris. This is exactly the sort of information I was after. I'll definitely check /recalibrate against lab-checked buffer solutions as you suggest.

Thanks